OEM versions are tied to the ystem they are first installed on; upgrade the motherboard, buy a new Windows.
Full retail let's you carry on on new system... kinda:
I recently swapped motherboards and reinstalled, now Windows won't activate. I can call some support line, but I'll be damned if I'm going to pay even 1 cent for support after buying that overpriced piece of plastic. I can go through some support center where I need to enter PID, but of course it doesn't accept it because it's still tied to my old board. You can continue without entering it, but then you are faced with the possibility of being charged €72,- (it's never made clear whether or not these costs will be waved if they establish you have a legal copy).
Long story short, OEM is tied to 1 system forever, retail can be installed on any system, as long as it's only 1 at a time.
Would be nice if they had some deactivation system to use before upgrade.
