Microsoft recently made available the Release Candidate 1 (RC1) update for x64-based versions of Windows Server 2008. To get the latest bits (in a Microsoft update installer package), go to Update for Windows Server 2008 x64 Edition (KB950049) at the Microsoft Download Center. If you’re performing remote administration from a 32-bit edition of Windows Server 2008, you can also download the RC1 update for 32-bit machines (remember that Hyper-V itself runs only on x64 machines that have virtualization CPU extensions).
To get more details on what is new and what has changed, see the Release Notes for the RC1 Release of Hyper-V document. The associated Knowledge Base Article 950049 also describes issues for updating, including the incompatibility of snapshots made in previous beta/RC releases of the product. You also want to upgrade VMs to the latest version of Integration Services (included with the update).
