I really like the artwork, very subtle color use, yet tasteful, and well-coded of course.
About the lemming: maybe you could draw like straps around his body, so it looks like the sign is strapped on instead of surgically grafted to his spine...? Maybe that won't put off the lemming-enthousiasts a little less...
On IE5.5/Win2000 there was a very slight bright line underneath the menu bar, and as you said when resizing the text to biggest, the "contribute" button wrapping around to the next line throws everything way off. You could either make the criss-cross background image tile and position the trees separately, or extend the current background image to compensate for the extra height. I don't know if explicitly setting a height for that div will work, though, and the list items need more room vertically as well (when they wrap, the next line partially overlaps the first one).
By the way, congrats on being the first bright one to spot the new forum!
@George: great thinking!