You’ll have to show us some more of your css and html so we can get an idea of the structure you have.
You should be absolutely placing #nav as far as I can tell and not the inner ul anyway.
Show us the html structure you have - you should be soing something like this:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
<style type="text/css">
#test {
padding-top: 50px;
width:760px;
margin:auto;
position:relative;/* needed for stacking context */
border:1px solid #000;
}
ul#nav {
position: absolute;
top: 0;
left: 0;
margin:0;
padding:0;
border-bottom: 5px solid #453d34;
width:760px;
list-style:none;
text-align: center;
font-size: 21px;
}
ul#nav li {
margin-left: 15px;
display: inline;
}
</style>
</head>
<body>
<div id="test">
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras interdum tincidunt leo nec placerat. Nam diam enim, pretium id ullamcorper eu, ullamcorper dictum nisl. Aliquam eget nisl mauris. Sed commodo euismod purus. Nullam vulputate interdum metus sit amet sollicitudin. Mauris bibendum nunc consequat nibh dignissim quis consectetur leo vestibulum. Phasellus nec neque a tellus fermentum euismod ac eget ante. Quisque et libero lorem. Etiam quis felis varius nibh fermentum feugiat quis sed lectus. Vivamus dui quam, bibendum eget bibendum nec, imperdiet quis leo. Integer nec nibh eu felis fermentum laoreet vel ac orci. Mauris eu velit nulla. Phasellus bibendum, augue sed ornare tincidunt, erat metus dignissim tortor, sit amet bibendum est magna vel mauris. Pellentesque sapien eros, rutrum eleifend porttitor cursus, aliquet in velit. Mauris erat leo, accumsan vitae feugiat eget, rhoncus sit amet ipsum. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Etiam porta, nunc et luctus tristique, libero ligula venenatis justo, eu consequat odio ipsum eget dolor. Etiam condimentum, justo eu viverra sagittis, erat odio mattis tellus, elementum aliquet diam tortor vitae libero. </p>
<ul id="nav">
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
<li><a href="#">menu</a></li>
</ul>
</div>
</body>
</html>