Have you tried the WIM2VHD tool?

WIM2VHD is a tool that will create a bootable VHD from a Windows 7 or 2008 R2 WIM image without having to run Windows Setup. You can create a virtual hard drive, mount it in Windows 7 or Server 2008R2, and then use this tool to install the operating system on that drive. That’s much faster than starting up the VHD in Virtual PC, Virtual Server, or Hyper-V and then installing using steup. You can use WIM2VHD to install from install.wim, which is the image used to install Windows, or you can apply a custom image to your VHD if you wish.

Why would you do this? Well, if you want to use the “Boot to VHD” capability of Windows 7 and Server 2008R2, you will need a VHD that contains your second OS. With WIM2VHD, it’s easy to install the OS in the VHD.

You can read about the WIM2VHD tool at http://code.msdn.microsoft.com/wim2vhd, and click the “Downloads” tab to download it. It’s pretty well documented, and the documentation is all downloadable from there as well.

Microsoft fully supports virtualizing Windows 7 and Server 2008 R2, but this tool is NOT supported by Microsoft, so you will have to read the documentation closely. Have fun!