If you work with Windows Server 2008 Hyper-V and Windows Server 2008 Failover Clustering, you should check a new update called "Increased functionality and virtual machine control in the Windows Server 2008 Failover Cluster Management console for the Hyper-V role". This hotfix includes a few key improvements on the way Windows Server 2008 Failover Cluster Management makes your Hyper-V virtual machines highly available, including:

• Changes to the virtual machine view
• Changes to virtual machine actions
• Allow for more than one virtual machine in a "Services or Applications" group
• Add support for mount points or volumes without a drive letter
• Changes to the virtual machine refresh action
• Behavior changes if any node of the failover cluster has a disconnected virtual machine
• Behavior change when you add a pass-through disk to a virtual machine
• Behavior change when the parent differencing disk is not on shared storage
• Volume path copy

Check all the details and request the hotfix download at http://support.microsoft.com/?id=951308