Swapping XP & Vista Around on Computers

I have a PC running XP, and I've just got a new laptop with Vista installed. Since I use the PC more often, and I realise you can't simply install Vista on both if you have only one Vista disc, is it possible to swap the OSs around? And if so, how?

 

Having just one Vista disk (I assume you mean a CD or a DVD) is not the problem. That one disk can be used multiple, even thousands of, times. It is identical of the tens of thousands of other disks out there. The problem is the product key, which is only to be used on one PC at a time.

 

The laptop version of Vista will be OEM, wheich means it cannot transfer to any other PC, it dies with the laptop