Emlékem szerint Vista pro és Win7 pro-tól felfelé 1 fizikai + 4 virtuális gépen használhatod ugyanazt az OEM licencet.
Közben utánanéztem:
"For Windows operating system software licensed through retail (FPP) or preinstalled on a PC (OEM), Windows use rights are outlined in the Software License Terms that accompany the software. These license terms provide use rights to run Windows locally on the licensed device in a virtual operating system environment (OSE); however they do not provide use rights for accessing Windows running remotely in a virtual OSE from the licensed device, and are limited in other ways..."