Section 3(d) of the license terms for my copy of Windows 7 64-bit Ultimate
(which are found in: C:\Windows\System32\en-US\Licenses\_Default\Ultimate) read:
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.
(Emphasis on "instead" is mine.) So you will need a separate license to run a copy in a virtual machine.