The “Import Virtual Machine” option under Hyper-V only permits the import of virtual machines previously exported from Hyper-V itself. You are out of luck if you are looking to use this as an accelerated means (as there is none officially from Microsoft) to conveniently import existing virtual machines (configurations defined in .vmc) created by Virtual Server 2005 or Virtual PC 2007. Read more here.
Nevertheless, you can reuse a virtual hard disk (.vhd) under Hyper-V by running the New Virtual Machine Wizard and provide similar settings as recorded in the .vmc. After this manual process, a folder tree structure (path changeable at point of creation) describing the new VM configuration will be created. The .vmc configuration file is deprecated. Although highly recommended, it is not necessary to first uninstall the Virtual Machine Additions. Installation of the Hyper-V Integration Services is required if services such as OS shutdown or time synchronization were to be made available to the guest OS.
For Windows XP and later editions that are subject to Windows Product Activation, you may be prompted with the following as soon as the VM starts:
This condition may appear even though it is a direct reuse of previously created .vhd that are already WPA activated from either Virtual Server or Virtual PC, where the VM’s hardware attributes such as CPU type/speed, RAM memory, hard-drive controller type (IDE/SCSI), network adapter type, etc. were not modified at all and no new hardware was explicitly added either.
Therefore, if you can help it, do not activate any previous versions of .vhd prior to bringing them under Hyper-V. If possible, build supported, RTM versions of the Windows operating system from scratch straight away on the target host machine running Hyper-V.
Tested on Windows Server 2008 x64 RTM with Hyper-V RC0 + KB949219