[Roanon]

No question - use 2000. XP only if you are an expert and know every option and how to turn them off (some of them are carefully mis-phrased and look like turned off when actually on). Or if you don't mind to be spied upon more than any trojan virus does, forced unwanted "updates" on you, and suffer random disabling of non-M$ programms.
Do not forget you cannot even turn off many spyware functions - even if they are made to appear to be off or non-working (like that "unregistered" XP JayBDay wrote about that has phoned home for sure). You have to install XP antispy to be at least a bit safe. Otherwise, M$ can reconfigure any of your settings as they like. I refuse to service any XP computer without antispy on it, and without expertly disabled update options. Apart from the overall personal security, such blatant violation of consumer rights should not be supported, IMHO.