I don't know if this will work on XP but I'll tell you anyway, it might still be useful. If youve recorded some files on WMP and when you move them to a different computer it wont let you play them because of "rights" management, heres what to do.
1.)Go to the PC you recorded the songs on, open WMP and go to tools, Rights Management (something like that)
2.)Whack in a floppy and tell it to back up to A:\
3.)Go to your other PC and tell it to restore it's rights from the disk

This worked great for me (with winME ans win98) and I hope someone out there finds it handy!