thats interesting...
I have WINXP PRO sp2 on 2 computers at home and have no problems whatsoever....except that they need rebooted about once a day and the older one tends to be a bit slow from time to time, but its over 3 years old now...
I never have to reboot any of my machines unless a critical patch really insists - I leave them running 24 hours a day. I really have tried to give FF a chance but it grinds my machine to a halt until I kill it off. Thunderbird is just too annoying to use.