I have a friend who wanted me to upgrade his HP laptop to windows 7. So I installed clean install retail copy of it on his laptop. The problem is, he needs his own license key for this laptop. I was wondering whether the system builder's license would work on a retail version installation? Or would I have to completely reinstall windows again to do this, using the system builder's license disc? It would save him a lot of money to have the system builder's license as opposed to the full retail version.