On May 15, 2008, Microsoft announced a Service Pack 1 update for its Microsoft Virtual Server 2005 R2 server virtualization product.
This update for Microsoft Virtual Server R2 SP1 includes support for the following additional Host and Guest Operating Systems
Additonal Guest Operating System support:
Windows Vista® Ultimate Edition with Service Pack 1 (SP1)
Windows Vista® Business Edition with Service Pack 1 (SP1)
Windows Vista® Enterprise Edition with Service Pack 1 (SP1)
Windows Server® 2008 Core
Windows Server® 2008 Standard
Windows Server® 2008 Datacenter
Windows Server® 2008 Enterprise
Windows Server® 2008 Small Business Server
Windows XP Professional with Service Pack 3
Additional Host Operating System support:
Windows Vista® Ultimate Edition with Service Pack 1 (SP1) (non-production use only)
Windows Vista® Business Edition with Service Pack 1 (SP1) (non-production use only)
Windows Vista® Enterprise Edition with Service Pack 1 (SP1)(non-production use only)
Windows Server® 2008 Core
Windows Server® 2008 Standard
Windows Server® 2008 Datacenter
Windows Server® 2008 Enterprise
Windows Server® 2008 Small Business Server
Windows XP Professional with Service Pack 3 (non-production use only)
Download it, here.