Wouldn't work on Virtual PC (HAL error), but I got it working on Hyper-V Manager 6.1.7600.16385. Very quick install - around 8 minutes.
It seems very hard to use without a touch screen, though. I haven't yet worked out how to close any of the programs I open because they are all full screen - I guess I'm missing a Menu hardware button. I've resorted to killing each one with Task Manager (via Ctrl+Alt+Del) and then using Task Manager's App History tab to start some of the others - I've lost the Metro Home screen somewhere! Oh, wait, if I click on the blank screen I get after killing an app it reappears!
Some of the sample apps also seem to use 100% CPU (the graphics-intensive ones in particular) and that brings the VM to a stuttering halt.
That Start screen is going to get some getting used to, though. Every time you hit Start the whole desktop disappears to be replaced by the Start screen...