I've been running XP Pro on this box since the summer of 2002 and it's been just fine. The only complexity I ran into was when my hard drive failed. I had a 120G drive that I imaged over to a 160 as a backup with the thought that I could just swap in the backup if the primary failed. Bill says "No" and the upshot was alot of headaches and hacking, but I think it's the same with Win2K, too.
It isn't. XP was when all the "fun" started.