Update March 19, 2008

This article on Microsoft site describes the Hyper-V Release Candidate update for Windows Server 2008.

The Hyper-V Release Candidate update to the Hyper-V role provides improvements in security, in stability, in performance, in user experience, in forward compatibility of virtual machine configurations, and in the programming model. All users of the Hyper-V role are encouraged to apply this update.

Please read the Article ID: 949219 on Microsoft TechNet site, you can find links for download

the update for x32 and x64 platform more than release notes