Upgrade with family pack

I want to buy the family pack to put on 3 PC's. One has Vista 64 bit, one has Vista 32 bit, and the last has XP. Is there a difference in the packages or is the "upgrade" meant for anything? Can i use the upgrade for my PC's?

I upgraded a PC with Vista 32bit & a laptop with Vista 64bit with the family pack so I'm pretty sure it would work for an XP upgrade as well.

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