Corporate licenses don't work the way they used to. In XP you didn't have to activate or anything. With Vista Microsoft now requires a corporate activation server, if you don't check in parts of your OS become disabled.. I wouldn't go there
Where there's a security measure, there's a crack. But I wouldn't go to Vista yet anyway; it's bloated, slow, and in serious need of patching. I'm personally not touching it until SP1.