A humerous article appeared on slashdot today, with the typical Windows bashing that’s to be expected.
But for my own reference, and hopefully the benefit of others:
Windows Vista Home Basic and Home Premium cannot be ran on a virtual machine legally, whether that be Linux, Apple or even Windows 95.
Windows Vista Home Basic and Home Premium cannot run a virtual machine of itself using the same licence (eg. Installing Vista Home Premium onto a new PC, and then install it again in Virtual PC with the same product key).
This is the same as Windows XP Home.
Windows Vista Business, Enterprise and Ultimate have virtualisation rights, which means that it is legal to run the same copy of Windows, with the same licence key in a virtual machine.