Some xp drivers work on 7, most don't. Also unlike user space, you cannot run 32 bit drivers on 64 bit windows, so unless you were running 32 bit win7 you needed 64 bit xp drivers, which were rare. Are you sure you explicitly installed xp drivers and didn't just happen to have hardware where windows shipped matching drivers or could download them from the windows driver database? (Or downloaded an installer bundle from the manufacturer's website that just contained drivers for all supported platforms..)