Centering my content in CSS/XHTML

Well I did some coding the other day. I did it all perfect as it seemed Valid, Tableless, Error free XHTML!

But then I viewed my work and I got my background image to center perfect, but for some reason I cant get my Content to center with it. I tired inputing my own "px" poistion and it works fine with my resoultion, but mucks up in other screen sizes.

I was wondering if anyone could take a look at it and tell me how to center my content with the background image?

Regards;
Justin

http://www.atstudios.roxr.com/sale/001/index.html
http://www.atstudios.roxr.com/sale/001/working.css