I have seen several methods for creating simple fixed width single column layout using CSS. I like the one shown here because there is very little code involved and it works on every browser I have tried.
margin: 0 auto;
...entire layout goes here...
The "margin: 0 auto" is the best way to do it, you just have to be sure to have the right doctype for it to work. I always use XHTML strict - others will work too. If you don't have a good doctype, the content won't center in IE6
To implement the XHTML strict doctype, put this above your node, as the first line in the page:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">