If you haven't already checked it out, be sure to jump over to Ben Armstrong's blog site, Virtual PC Guy, and read up on his latest three posts about using Powershell to help with Microsoft Virtual Server.
He uses Powershell to query guest operating system information. Go look at his Powershell script, which seems much easier than his older VBScript to do the same task. Go here.
Using Powershell, Ben offers a script to list the available virtual machines on a system. Check it out, here.
And his latest script uses Powershell to examine the virtual hard disk information. You can find this script, here.