Google Chrome won't run (or install) on Win2k (at least not without hacking). Firefox is nice, but seems to continue to have huge memory leaks (at least with TabMixPlus). It's time to try something new (to me) - I last looked at it briefly when it was still payware.
So far, so good. Opera 9.6 is worth checking out if you're not happy with the usual suspects.
http://www.opera.com/download/
Cheers,
Scott.
(For Wade, it is to Evangelize the Opera! :-)