Corporate is the best solution to your, ahh, problem. It is meant for companies that are doing mass cloning operations and do not want toregester hundereds of copies. That said, if call up M$, they will fix most of your porblems with only a few questions (I gave a friend an extra copy of XP Home I had and it refused to regester, a call fixed it)
Do not try an activation crack. There a a lot of fake ones out there, and they can contain particurally nasty virii.
Also, you may have issues with automatic update with mutliple installs.