CSS Mac Woes

Brian wrote in with an analysis of my CSS problem. Apparently IE5 and Safari on Mac ignore a "top:50%" setting in the div that aligns things vertically and horizontally. He reports that Chimera works fine, but I'd like to find a way to make it work across all browsers. I might have to play around with some JavaScript navigator.userAgent selective writing. But I wouldn't be surprised if that opens a whole new can of cross-browser headaches. I think my best course is to go back to using tables for layout.