I downloaded the Orcas Visual Studio Beta 1 VPC from MSDN yesterday and stitched all of the zip files together, and launched it. Ran into the dreaded:

“E:VPCTimeBombedBaseBase01.vhd” could not be found message. If you run into the same thing, you can find others with the same issue easily enough.

The solution is to download the VSCTPBase.exe file from here. Extract the Base01.vhd file and then point to that as the base for your Orcas VPC. It’s working great for me now.