Eu tropecei nessa questão e fiquei curioso sobre o Windows 7 Professional (meu caso).
Acho que o EULA (a ser encontrado aqui ) responde a essa pergunta conclusivamente. Abaixo, veja as partes relevantes (mais notavelmente 3 / d).
1. OVERVIEW.
b. License Model. The software is licensed on a per copy per computer basis. A computer is a
physical hardware system with an internal storage device capable of running the software. A
hardware partition or blade is considered to be a separate computer.
2. INSTALLATION AND USE RIGHTS.
a. One Copy per Computer. The software license is permanently assigned to the computer with
which the software is distributed. That computer is the “licensed computer.”
3. ADDITIONAL LICENSING REQUIREMENTS AND/ OR USE RIGHTS.
d. Use with Virtualization Technologies. Instead of using the software directly on the licensed
computer, you may install and use the software within only one virtual (or otherwise emulated)
hardware system on the licensed computer. When used in a virtualized environment, content
protected by digital rights management technology, BitLocker or any full volume disk drive
encryption technology may not be as secure as protected content not in a virtualized
environment. You should comply with all domestic and international laws that apply to such
protected content.