Well your attachments havent been approved yet but Ill try some preliminary help and HOPEFULLY wont make a boob out of myself! 
OK, question 3 is actually a LOT easier than you think .... works like a charm and it has the Paul O stamp of approval (our resident CSS god)
Code:
body {
text-align: center;
margin: 0px;
padding: 0px;
min-width:775px;/* stop mozilla sliding off the edge */
}
.central {
margin-right: auto;
margin-left: auto;
position: relative;
width: 775px;
text-align: left;
}
and then create this as your outer container:
Code:
<div class="central">
all the rest of your page.....
</div>
This and MANY more great CSS "must knows" are found in this thread:
http://www.sitepoint.com/forums/showthread.php?t=171943
#2 - as I said I CANT seen you images yet but the best way IMO would to be use lists (ul) ... each button is an li element of the list and you can adjust them according to what you need for padding, margin etc etc ... and if you use the proper html mentality what is a Menu? hmmm? Is a LIST of sections in your site (or a list of links to sections of your site)
Now as far as #1 Im at a loss cause I cant see the attachments BUT again Ill give it a shot.
Sounds like you are looking for floated divs (3 across), each with their own width but my question would be are the absolute widths or percentages? Anyways a REAL QUICK "guess" at what you are trying:
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html lang="en" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
<title>really Simple 3 color col example</title>
<style type='text/css'>
body {
margin: 0;
padding: 0;
}
#left {
width: 25%;
height: 500px;
background-color: RED;
float: right;
}
#middle {
width: 50%;
height: 500px;
background-color: GREEN;
float: right;
}
#right {
width: 25%;
height: 500px;
background-color: BLUE;
float: right;
}
</style>
</head>
<body>
<div id='right'></div>
<div id='middle'></div>
<div id='left'></div>
</body>
</html>
Now, thats a REAL simple example cause Im not sure what you are doing. Note I run the divs from right to left..... Paul taught me this to help deal with the dreaded IE drop and it does help (albeit takes a while to get used to!)
Theres a ton more to learn but hopefully this will get you started!
BTW, congrats on getting "off" the DW thing ....... a wonderful cause and idea! (wish more would do it!) ... it can be tough at first but man once you have it down you will laugh at DW! 
Learning the DIV-idends!
Lots of other CSS tutorials listed on the site - they will help you with the answers you posted.
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