I just learned this the hard way, but if you’re trying to take advantage of Windows 7’s Boot From VHD feature, you need to keep one thing in mind. Boot From VHD is only supported when Ultimate or Enterprise are the OS on the VHD. I just tried to install Professional, and got this nice error during startup:
License Error: Booting from a VHD is not supported on this system.
Just putting this out there in case you were considering doing boot to VHD.