Recently I had some major issues with a VPC somebody prepared for me. It came from a DVD and I just could not get it to run on Vista, though it ran great on XP. I was fairly sure that it would run OK if I could just launch VPC elevated and then open the .vmc file, but when I launched VPC (elevated or not) the only evidence of its existence was a taskbar entry (there was no window to be seen) and even that disappeared if I right-clicked on it.
I solved the first problem by granting Users access to the .vmc and .vhd files (I went with Full Control since I had them on a non-shared drive) and then the VPC ran perfectly. That was a better fix than elevating VPC every time anyway. But along the way I discovered how to fix the disappearing console. This post by Steve at EssJae.com shows what you need to do: find the options.xml file in C:\Users\%current_user%\AppData\Roaming\Microsoft\Virtual PC and open it -- make sure the console is not up and you're not running a VPC. Scroll down and find the <console> section and you will see some very large numbers for left_position and top_position. Change them to something normal, like 10 or 100, and save the file and you'll be back in business.