Originally Posted by Amputate Your Head

That sounds awfully complicated.

Why not just remember to keep your width at 1000px or less so you avoid horizontals on 1024x768's, and then make a small seamless repeating bg so you don't even need to worry about whether your bg is going to be an issue. Making a fixed size bg (whatever the size is) is always going to be a problem somewhere for someone. Just eliminate that issue up front.