I've been working with Virtual PC on a new project and have had difficulty with one of my Virtual Machines (VMs). When I shut it down, it just hung on the shutting down message:
"Windows is Shutting Down..."
This particular VPC was one provided by Microsoft, and included Windows Server 2003, Sharepoint Services, Sharepoint Portal Server, Exchange, Active Directory, the kitchen sink, etc. [grin].
Well, it turns out Exchange was the culprit. The first few times I attempted to shut down the VM, I got impatient and just forced it closed. When I finally waited, it shut down on its own. It took 10-15 minutes, but it DID shut down cleanly.
Patience is a virtue...