After announcing the availability of the updated Hyper-V bits last night, Microsoft has finally enabled the download at the Microsoft Download Center.
The Release Candidate 0 (RC0) update to the Hyper-V role provides improvements to security, stability, performance, user experience, forward compatibility of configurations, and the programming model. All users of the Hyper-V role are encouraged to apply this upgrade. After you install this item, you may have to restart your computer.
Hyper-V, Hypervisior, Release Candidate, Windows Server 2008, Download