For those upgraded to RC1 and attempting to run Virtual PC, you might get the following error message:
Virtual PC could not open the Virtual Machine Network Services driver
To resolve, right click your network connection and then select properties>install>service>add and select the Virtual PC Network adapter. If it is not present it is found at the following path assuming you installed on the C:
C:\Program Files\Microsoft Virtual PC\Utility\VMNetSrv\VMNetSrM.inf
That should resolve the issue once you restart Virtual PC.