Hyper-V RC1 is readily available. You can find more details here: http://blogs.technet.com/virtualization/archive/2008/05/20/hyper-v-rc1-release-available-on-microsoft-download-center.aspx. The link to the Microsoft Download Center is http://www.microsoft.com/downloads/details.aspx?FamilyID=3ed582f0-f844-40ba-b692-230845af1149&displaylang=en.

Virtual Server has also been updated and Win2k8 is now qualified as a quest and a host operating system. For more details, see http://www.microsoft.com/downloads/details.aspx?FamilyID=a79bcf9b-59f7-480b-a4b8-fb56f42e3348&displaylang=en.

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)