as long as windows xp is activated, there is no problem. the only other problem that might happen would be when you try to run windows update.
in my travels on the internet, and talking to people, if there is a copy of windows xp that isnt legit in the purest form, the hardest part to get it running is activation. i have also heard that for some reason windows xp corperate edition doenst need to be activated, just a cdkey. i wouldnt happen to have had any encounters with such though
back on subject though, do you have mcaffe privicy service, or something similiar? for some reason, it shows nothing but gibberish on the page until i disable it, then it works fine. have fun