Q. What are the virtualization license rights for Windows Server 2008?
A. The virtualization rights with Windows 2008 haven't changed from Windows Server 2003, except for Windows 2008 Standard. In Windows 2008 we have the following versions:
Standard Edition - One physical instance and one virtual guest instance running at same time. This is new in Windows 2008.
Enterprise Edition - One physical instance and four virtual guest instances running at same time
Datacenter Edition - One physical instance and unlimited number of virtual guest instances running at the same time.
It's this new 1 + 1 licensing for Standard that makes the new Microsoft Hyper-V Server purchase attractive only if you want a virtualization server running guest OSs that are not Windows Server. That's because Windows 2008 Standard has one virtual license and a full server capability on the server. It's not just restricted to Hyper-V, it could have additional roles added in the future or repurposed. If you want Windows 2008 just for virtualization, buy the Standard version and install in its core mode with only the Windows Server Virtualization role, which is essentially what Hyper-V server will be.