Virtual machines have few if any requirements above those required to run the operating system. If the operating system has not been optimized for the virtual machine host environment, the unmodified OS can run only on hardware-assisted virtualization computer hardware, in full virtualization mode, and requires specific device drivers to be loaded.
You should be aware of any licensing issues related to running a single licensed copy of an operating system on multiple virtual machines. Consult the operating system license agreement for more information.