Attempts by Microsoft to increase demand for Windows Vista led to changes in the licensing rules of the operating system. Starting from yesterday, business users can legally run Vista on diskless PCs. Thus, several personal computers connected by a network act as a physical computer, and the operating system itself can be run on the server.
This type of license will be included in Windows Vista Enterprise, but not in the others.
In addition, Windows Vista Enterprise can be virtualized on servers, but this option will require additional fees. ')
via CNet