I've tried that too, I'll include the relevant code, hopefully it'll make answering easier 
Code:
#sidebar {
width: 150px;
float: left;
margin: 5px 0px 10px 10px;
padding-top: 50px;
text-align: center;
}
#content {
width: 700px;
float: right;
margin: 5px 15px 10px 0px;
padding-top: 20px;
padding-bottom: 20px;
background-image: url(images/watermark.bmp);
background-repeat: no-repeat;
background-position: center;
}
#footer {
clear: both;
width: 880px;
margin: 0px;
padding: 10px;
text-align: center;
border-top: 1px dotted #cccccc;
And here's how it's used in HTML:
HTML Code:
<div id="sidebar">
<p>Sidebar Stuff Here</p>
</div>
<div id="content">
<p>
Content Here
</p>
<div id="footer">
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