CSS/XHTML Centering

I’m building a site in XHTML and CSS for a friend. I’m using embedded tables for the layout and it’s working fine.

I need to know if there’s a way to center the entire page in the browser window (like this forum is) without using the align=“center” (which this forum uses), which would invalidate it since I’m using the XHTML Strict DTD.

I don’t think it can be done with CSS positioning, but my understanding of positioning is not very in-depth, since tables with defined widths for cells do it for you. Eventually, I need to really get down to it and read through my CSS and XHTML books again.

Suggestions? Thanks in advance.