I had to "play" around with some Virtual Machines under Hyper-V and Server 2008 R2. I encountered a number of issues when moving and re-importing VMs.
Typically you just use the export and import functions, but being a tech, I always curious what is happening under the bonnet.
These articles helped me at various stages of the project:
Moving a Windows Server 2008 Hyper-V virtual machine by Ken Schaefer
Hyper-V VM fails to start after moving the VHD files by Mat Mirabito
Hyper-V Disk Size Reduction posted by Boris on May 08, 2009 on Technet
When I re-created a VM from scratch using only the VHD file, I had an issue with the VMs networking. When the VM started, it claimed to be connected to an "Unidentified Network". There was no way I was able to change the setting. I tried various ways to resolve this. Narrowing own the isse I found that the problem somehow was with the actual physical port on the switch. I deleted the virtaul network in the host and disabled the network adapter in the VM, then plugged the cable into a different switch and recreated the virtual switch and reconnected the VM.