I've noticed this problem with IE 5.5 at home, though it works at work. Strangely, it fails to load images correctly at work.

If you're using IE, change your security settings to turn off Javascript, close IE and then get back into it. Change them back and try and login. That's how I solved it. Something was screwed up with the cookie settings but it worked itself out.

If your using another browser, I have no idea what it could be. Netscape 4.77, 6, Opera, and Mozilla all work for me here.