Okay i downloaded you page and I have made a few changes so that it will be more valid. There were a few errors preventing it from working properly. Here is the html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Oberlin Design: design2 Table layout</title>
<link rel="stylesheet" type="text/css" href="odgreyellowtable.css">
</head>
<body>
<div class="wrapper">
<table>
<tr><td colspan=3 class="header">
<img src="http://oberlindesign.zxq.net/greyellow/header1.jpg" alt="Oberlin Design Greyellow Header" align=left><p>
This is the welcome text for Oberlin Students for Art and Design; Oberlin Design. words and more words go here for ever and ever and ever and more and more words and wait could it be? even more words. that should be about enough. </p>
</td></tr>
<tr><td class="divider" colspan=3>
<br><hr><br>
</td></tr>
<tr><td class="contentBox">
<P>member bios</p>
</td>
<td class="contentBox">
<P>upcoming projects</p>
</td>
<td class="contentBox">
<P>application process</p>
</td>
</tr>
<tr><td class="divider" colspan=3>
<br><hr><br></td></tr>
<tr><td colspan=3 class="header">
<P>footer goes here with contact information</p>
</td></tr>
</table>
</div>
</body>
</html>
and here is the revised css
/*
your contact info
*/
body {
font-family:Georgia, "Times New Roman", Times, serif;
font-size: 12px;
color: #a7a7a7;
background: #717576;
text-align: center;
}
p {
color: #a7a7a7;
font-family: Georgia;
font-size:12px;
}
div.wrapper {
margin-left : 10%;
margin-right : 10%;
}
table, tr, td {
padding: 15px;
border: 0;
margin: 10px;
border-spacing:20px;
}
td.divider {
background: #717576;
margin-top: 10px;
margin-bottom: 10px;
text-align: center;
}
td.header {
background: #626666;
border:0px;
}
td.contentBox {
background: #626666;
border: 0px;
border-spacing:20px;
width: 33%;
}
hr {
color: #ece87d;
background-color: #ece87d;
width: 65%;
height: 5px;
border-style: dotted;
border: 1pt dotted #ece87d;
}
this will validate ( totalvalidator) and does not throw css errors in the firefox console so it's a better starting point.
I can see that it is not looking exactly the same now but you can tweak it from there. Now you have things working with the background anyway. I suggest using the validator regularly as you go along it is helpful in getting things right. I might also have made some mistakes though, I normally don't do tables.
If you plan for an important website that you will be spending a lot of time on you might save yourself some trouble in the long run if you change the layout from being table based to using divs instead.