Hi,
This seems like Deja vu but here goes again 
You need to explicitly control the margins and padding of all elements as they have different defaults between browsers. The form element for example has a large margin that will upset layouts if not rectified. So always control the margins and padding of your elements.
The other issues, that will show when you are doing something wrong is that you have specified a height in some cases that is too small to contain the elements. When you do this mozilla says "hang on" I don't fit and therefore doesn't fit. IE on the other hand says "poor chap doesn't know what he's doing so I'll help him along and increase the div to fit the content".
So because you have specified the wrong height then you have different variations between browsers. Had you correctly defined the height then there would be no difference and everyone would be happy.
One of the places where you have gone wrong is that you have specified a line-height of 2em in the body therefore the smallest ie will render an elements height will be 2em (unless you specify overflow:hidden). As you have only allowed 15px for your sub-header (which is about 1em) then that is why you have such a variation between browsers as ie will expand to 2 em and mozilla wont.
I have amended some sizes to show what I mean but I realise that I may have amended them in the wrong direction for your layout but the example will show you how things even out when there are no conflicts.
This is not meant to be a full solution but a pointer in the right direction.
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css">
html
{
height:100%;
}
a {
color: #3366CC;
text-decoration: none
}
body {
background-color:#FFFFFF;
font-family: Arial, Helvetica, sans-serif;
font-size: 1em;
color: #000000;
margin-top: 0.1em;
margin-right: 0.1em;
margin-bottom: 0.1em;
margin-left: 1em;
height: 100%;
}
.SectionTitle
{
color: #000000;
font-size:larger;
font-weight:bolder;
background:#405080 url(http://www.myhattiesburg.com/images/secthead1.jpg) repeat-y left top;
text-align:center;
height:21px;
margin:0px;
padding: 0px;
}
.SectionBox
{
color:#000000;
background-color:#FFFFFF;
border: thin #000000;
border-style:solid;
height: 195px;
background-image:url(http://www.myhattiesburg.com/images/boxheader.jpg);
background-repeat:no-repeat;
margin:0;
padding:0;
}
.boxTitle
{
position:relative;
top: 0px;
color:#000000;
text-align:center;
font-size: 0.9em;
line-height:0.9em;
font-weight:bold;
vertical-align:top;
}
#header
{
position:relative;
width: 750px;
height: 70px;
background-color:#FFFFFF;
}
#subheader
{
position:relative;
width:750px;
height: 20px;
line-height:20px;
background-color:#5C73B8;
color:#FFFFFF;
font-size: 0.9em;
font-weight: bolder;
margin: 0px;
padding: 0px;
}
#search
{
position:relative;
top: 0%;
left: 0%;
margin: 0px;
padding: 0px;
}
#main
{
position:relative;
left: 0%;
width:750px;
}
#topdiv
{
position:relative;
margin-top: 1%;
left: 0%;
width:750px;
}
#toprow
{
position:relative;
left: 0%;
top: 1%;
padding-bottom: 5px;
padding-top: 5px;
width:750px;
height: 195px;
}
#t_links
{
position:absolute;
left:0px;
width:120px;
display:inline;
border-right: thin dotted #405080;
}
#t_lbox
{
position:absolute;
left:130px;
width:200px;
display:inline;
}
#t_cbox
{
position:absolute;
left:340px;
width:200px;
display:inline;
}
#t_rbox
{
position:absolute;
left:550px;
width:200px;
display:inline;
}
#centerdiv
{
position:relative;
left: 0%;
top: 1%;
width:750px;
}
#centerrow
{
position:relative;
left: 0%;
width:750px;
height:195px;
top: 1%;
padding-bottom: 5px;
padding-top: 5px;
}
#bottomdiv
{
position:relative;
left: 0%;
top: 1%;
width:750px;
}
#bottomrow
{
position:relative;
left: 0%;
width:750px;
height:195px;
top: 1%;
padding-bottom: 5px;
padding-top: 5px;
}
#footer
{
position:relative;
left: 0%;
width:750px;
height: 35px;
}
#search form {margin:0;padding:0;}
#search input{height:14px;margin:0;padding:0}
#topdiv p, p.boxTitle {margin:0;padding:0}
</style>
<title>MyHattiesburg.com</title>
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_reloadPage(init) { //reloads the window if Nav4 resized
if (init==true) with (navigator) {if ((appName=="Netscape")&&(parseInt(appVersion)==4)) {
document.MM_pgW=innerWidth; document.MM_pgH=innerHeight; onresize=MM_reloadPage; }}
else if (innerWidth!=document.MM_pgW || innerHeight!=document.MM_pgH) location.reload();
}
MM_reloadPage(true);
//-->
</script>
</head>
<body>
<div id="subheader">
<div id="search">
<form name="f_search" method="post" action="">
Search
<input type="text" name="searchfield" accesskey="s" tabindex="1">
</form>
</div>
</div>
<div id="main">
<div id="topdiv" class="SectionTitle">
<p>Section One</p>
</div>
<div id="toprow">
<div id="t_links"> Links </div>
<div id="t_lbox" class="SectionBox">
<p class="boxTitle">Events</p>
</div>
<div id="t_cbox" class="SectionBox">
<p class="boxTitle">Last Forum Posts</p>
</div>
<div id="t_rbox" class="SectionBox">
<p class="boxTitle">Weather</p>
</div>
</div>
<div id="centerdiv" class="SectionTitle">
<p>Section Two</p>
</div>
<div id="centerrow">
<div id="t_links"> Links </div>
<div id="t_lbox" class="SectionBox">
<p class="boxTitle">Events</p>
</div>
<div id="t_cbox" class="SectionBox">
<p class="boxTitle">Last Forum Posts</p>
</div>
<div id="t_rbox" class="SectionBox">
<p class="boxTitle">Weather</p>
</div>
</div>
<div id="bottomdiv" class="SectionTitle">
<p>Section Three</p>
</div>
<div id="bottomrow">
<div id="t_links"> Links </div>
<div id="t_lbox" class="SectionBox">
<p class="boxTitle">Events</p>
</div>
<div id="t_cbox" class="SectionBox">
<p class="boxTitle">Last Forum Posts</p>
</div>
<div id="t_rbox" class="SectionBox">
<p class="boxTitle">Weather</p>
</div>
</div>
</div>
<div id="footer"> footer </div>
</body>
</html>
Most of the time css will work when thisngs are defined correctly. However the differences arise when there are conflicts and IE will always try to guess whereas stricter browsers will usually do exactly as they're told.
I hope that all makes sense
Paul
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