Are you sure?
I was under the impression (and I think I got that impression from CF) that with OEM Vista (not XP), you could only install it once to one computer. If you were to change out the motherboard, that would constitute as a "new computer" and it would ask for a new, different, license. Where as with retail, you could uninstall/install Vista as many times as you'd like. However, the easy way around it I have heard, was when the OEM asks you for a different license, just call up microsoft and tell them some b.s., like you just replaced a hard drive or something, and they'll no questions give you another license number.