It's Microsoft Virtual PC and a Windows XP install image. No CD key or license needed, it's completely free and runs great. Just don't expect to run games or anything that needs hardware acceleration or wants direct access to hardware. If it implodes or catches a virus just delete it and install it again.
I had to use it before I got my new camera - my old one could not connect to Windows 7 at all. So i used USB passthrough mode and connected it to the XP mode VM whenever I needed to transfer photos.