Help with virtual pc in windows 7

I am having a problem with virtual pc in windows 7. Specifically everytime i try to boot up windows xp in the virtual pc it will eventually shut down saying it has a problem. I was wondering if anyone could give me suggestions on this. Windows does not give any error messages other than the obligatory shutdown message, it says it will search for a fix but does not find one. I have tried to uninstall and reinstall, and have made sure i have the 64bit versions of both. I have also checked windows update with no luck. I am running Windows 7 RC on a phenom 2 720 with the hardware virtualization turned on. Any suggestions would be greatly appreciated.