>And I think WilliamK is wrong in his interpretation of "OEM" being for that system and only that system. I had to re-install XP with the new motherboard (the shop had installed their own on my C: while diagnosing my problems (with my permission)) and I had no trouble "activating" it after doing so.

My understanding of this has always been fuzzy. What defines THAT system? The mobo, cpu, hard drive, case? I haven't ever been able to find a definitive answer.