How sure are you about that Patchou? unless you try letting a 64bit Xp user test it without a version check? Most programs from the normal Xp work without trouble in 64bit Xp because they have thing which does an emulation (can't remember what its called and i've gotta go so i can't go reread the stuff)
but more info is here http://www.microsoft.com/windowsxp/64bit/default.mspx
also you can get your 64bit copy there.
