1) Micros~1 will hear "through the grapevine" of some system successfully virtualizing Vista. (The "grapevine" being some bigmouth blogger who just cant resist shooting of its mouth, or a hit on a bot that trolls eBay looking for someone selling virtualization solutions).
2) Micros~1 will then buy a copy for $pittance of said virtualization software.
3) When they determine that said virtualization software does indeed work, they will then figure out its fingerprint in much the same way that anti-virus makers detect a virus's fingerprint.
4) Micros~1 will then deliver countermeasures through their automatic-update-that-you-cannot-shut-off-without-violating-the-eula-remember-all-your-hardware-are-belong-to-us
"facility". Suddenly, said virtualization fails to work. (and probabaly downloads your MAC address to Microsoft through their phone-home-that-you-cannot-shut-off-without-violating-the-eula-remember-all-your-hardware-are-belong-to-us "facility".) (If they were smart [don't we all wish], they'd delay their de-virtualization patch activation until some time later than the download that actually bombs the virtualizer, so that one couldn't easily associate which download contained the bomb....