Concerning licensing and virtualization – the most important thing to know is that any guest operating system must have a license, just as any physical server or workstation does. Thus, if you run Microsoft Virtual Server on Windows Server 2003 and 3 guest operating systems are running (Windows XP, Windows Server 2008, and Windows Vista), you must have 4 Microsoft operating system licenses – Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008.
As Linux is typically open source, you can generally have as many Linux guest operating systems as you want without paying any licensing fees. Just make sure you following the license agreement for your operating system.
For more information on virtualization & guest operating system licensing, see:
- Microsoft Virtualization Licensing and Distribution Terms
- Unlimited Virtualization Rights with Windows Server Datacenter Edition
- Licensing Microsoft Server Products with Virtual Machine Technologies White Paper
- Licensing Server Products with Virtual Machine Technologies
- Multicore and Hyperthreaded Processor Licensing