I disagree completly. Servers are run on windows all the time. I've had a two and a half month uptime on XP professional (running apache, php, mysql, and gaming in general) and no problems. No memory hogging, no slowness.
I also has a 6 month uptime on 98 which ran a webserver and ftp but was not used contantly. It'd be over 6 months if it weren't for a power outtage some time january :\

Anyways, its all about who configures it and how they configured it. People who have repetative problems with running servers on xp/2k (imo) don't know how to run a server in the first place.

>:D