John has posted a good blog entry describing how to make vhd image work between VPC/Virtual server and the new windows server 2008 hyper-v based virtualization solution.

#Are VHDs compatible between Hyper-V and Virtual Server and Virtual PC?
http://blogs.technet.com/jhoward/archive/2008/02/28/are-vhds-compatible-between-hyper-v-and-virtual-server-and-virtual-pc.aspx