[Znod]

The only problem with what felix says is that I have determined uneqivocally that either approach violates the Vista EULA. Doing so is a matter of personal choice; I make no judgments--just provide info. Anyway another way to retain XP for an emergency, and to at least "give up" the product key, is to make a disk image of one's XP installation, for example, on an external drive. I sort of like this approach because you can argue that your approach provides a way to reinstall Vista cleanly in an emergency--which is wise because MS has not yet identified a way to do so. At least this way, if you did not use your XP except in an emergency, then you would be, IMO, slightly more in the spirit of compliance with the EULA.