Disk2VHD is a tool written by Microsoft’s Mark Russinovich of Sysinternals Fame. You can find our more here.
I had a issue that I couldn’t mount the VHD from Windows 8. It wouldn’t work because the VHD file was on a network share, this also happens if it’s on an external HDD. The VHD file needs to be on the local PC. Which is a bit of a shame. It would be really useful if this could be done. 🙁