Recent Hyper-V KBs
949219 Description of the Hyper-V Release Candidate update for Windows Server 2008
949222 Virtual machines that were created on the beta version of the Hyper-V role do not start after the Hyper-V role is updated to a later version
949758 Availability of the Windows Vista Service Pack 1 management tools for the Hyper-V release candidate
939853 You receive an error message when you try to upgrade the WSv preview build installed on Windows Server 2008 RC0 or on Windows Server 2008 RC1 to the Windows Server 2008 RC1 build with Hyper-V beta or to the release version of Windows Server 2008