Computing New Brunswick

XP did not have a specific limit for the number of times the license was transferable, but that Microsoft wanted to be “specific” about transfer rights with Vista.
A change Microsoft made to Windows client licensing since XP is that only two versions of Vista — Windows Vista Ultimate and Windows Vista Business — can be run as a virtual operating system in a virtual machine.
THESE ARE VERY EXPENSIVE!!!  something like $500!

http://www.networkworld.com/news/2006/101606-microsoft-allows-one-vista-transfer.html

Consumers will be able to transfer the operating system license they purchase to only one machine other than the one for which they originally buy Vista, said Shanen Boettcher, a Windows general manager at Microsoft. He said Microsoft thought the change made sense because “lifetimes for PCs are getting longer.” Most likely, a user will not need to transfer an operating system license to more than one computer during the time that operating system is the latest one available, Boettcher said.

Microsoft also has tightened up antipiracy features in Vista, and users who do not verify that their version of the operating system is authentic with a software license key within 30 days of its activation will lose the use of certain features of the PC until they do so. The company unveiled this characteristic of Vista, called its Software Protection Platform, about two weeks ago.
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I know this will cause problems. I have seen quite a few “this version may not be legitimate” notifications.
what a lot of people don’t reaize that reduced functionality means it’ll turn on and tell you it has a licensing problem then will only allow you to resolve that licensing issue and nothing else until licensing is resolved.