Xp Home to Xp pro

I just bought a new system that I requested xp pro instead of Vista, so I loaded xp pro on my old system. Is there anyway I can keep xp pro on my old system that originally has xp home? Microsoft says that I have 30 days to remove it. I realize the copywrite issues,etc, but thought maybe there was some way of doing it.Thanks

Ya lost me....If you used your OEM XP cd on another machine->you need to purchase another key code.

One machine per keycode.

Yes I know.Is there anyway of not shelling out more money for my backup? Thanks

Reinstall XP Home on it;)