Ah, I know what the problem is... You're trying to use Windows as a server ;-)
Don't get me wrong, WIN2K PRO is a wonderful OS, it's on all our machines here, and I never have to reboot. Our servers are hosted by Verio and are running FreeBSD.
If you can, try using Linux or another Unix based OS as a server, they are much much more stable and more secure. Other than that, i've run out of ideas as to what could be wrong.