Generally 1024x768 but, I took a look at 800x600 and 1280x1024. All seemed fine. 800x600 was a 'perfect fit'. At the others, the content was all on the left, would be just a little nicer if it were centered at those resolutions but, only if it would also still be centered in a reduced viewport. Like you could change this:
<DIV style="position:absolute; align="center; top:40px; z-index:0">
unless that messes other things up.
<DIV style="position:relative; align="center; top:40px; z-index:0">