I am about to get a new PC with Vista on it and I currently have XP Pro on my current PC. Is it possible to unregister my current XP Pro (I purchased it and have the key, and CD(s)) so someone else can register and then use it? THanks...

Unfortunately no; it is licensed to one computer and only one computer.
It's a bit unfair, but then, you can get an "upgrade" copy of Vista for less than the full version.

By the way, are you sure you need Vista? If you just want pimp up the look of Windows, you can buy
WindowsBlinds for $20 - there's a limited free trial version you can try out.

Vista is coming with my new PC so I'll try it out. I guess I can always go back if needed to XP. Thanks for the info...