It displays perfectly in IE 5 for Mac, but in Netscape 4.78, the rightmost column appears differently - the table cell under "Columns" goes down quite a bit farther than the last line of text, and the "Bookmarks" cell (with the black bacground) appears higher than it does in IE. And after looking at the HTML, I can't figure out what causes it - must be a Netscape - specific table thing. The "height" attributes don't work like they should.
To get around the problem, you could probably change the third column to be a table within the larger table (sort of like you've done with the first column), eliminating the need for extra rows, which might be confusing the browser somehow.