Re: Considering this build
After a delve into the official win 7 forums, and a brush with an uncomfortable amount of MS glad handing and legal-ese. I have an anwser, OEM versions lock to the motherboard, You can change everything else and retain the license, but if you change the motherboard a new license has to be obtained.
Overall, I'm fine with this. I don't build new pc's very often and I have no intention of replacing the motherboard for probably 2+ years (Unless it burns up or some other awful event).
And the rules may be loose, I remember my OEM XP disc and key were used on 4 or 5 separate builds