I found it. To get the version of Virtual PC that is running when you are on Windows 7, open a virtual machine and select the Help icon in the upper-right-hand corner of that window. Clicking that will show a drop down menu of three options. One of those options is "About Virtual PC" and that has version info.
I'm using Virtual PC 6.0.192.0 on Windows XP, so it could be different elsewhere. But in the Virtual PC Console go to the Help menu and select About Virtual PC...