There is a way, but i don't think it's legal to post it here.
I asked the same thing to a friend since i didn't have my own CD-Key. And i'm running on XP Home now
But i used the legal way since i don't really like pirating stuff, i jsut got M$ to renew my key over the phone. told them i corrupted my HDD and lost windows, and since it was an OEM key it wouldn't let me re-install. they understood and let me re-activate.