make a class of container as below in your css file
<pre lang="CSS">.container {
width: 900px;
margin: 0 auto;
}
</pre>
and proceed with the fallowing procedure in html
<pre lang="HTML"><div id="main">
<div class=container>
</div>
</div> </pre>
in id=main you can handle with backgrouds ar other stuff.
class container div centers the contents of web side.