Microsoft has released an update to the Hyper-V role for Windows Server 2008

The Release Candidate 1 (RC1) update to the Hyper-V role provides improvements to security, stability, performance, user experience, forward compatibility of configurations, and the programming model.

After you install this item, you may have to restart your computer. Once you have installed this item, it cannot be removed. This update is provided to you and licensed under the Windows Server 2008 License Terms.

Download for 32-bit
Download for 64-bit