Still no x64 guests support… 🙁
Hopefully we’ll soon see a beta version of "Virtual PC 2009" or "Hyper-V Desktop Edition" (Or whatever the name will be…), that supports 64-bit guests.
This update for Microsoft Virtual PC 2007 includes support for the following additional Host and Guest Operating Systems:
Additonal Guest Operating System support:
Windows Vista® Ultimate Edition with Service Pack 1 (SP1)
Windows Vista® Business Edition with Service Pack 1 (SP1)
Windows Vista® Enterprise Edition with Service Pack 1 (SP1)
Windows Server® 2008 Standard
Windows XP Professional with Service Pack 3
Additional Host Operating System support:
Windows Vista® Ultimate Edition with Service Pack 1 (SP1)
Windows Vista® Business Edition with Service Pack 1 (SP1)
Windows Vista® Enterprise Edition with Service Pack 1 (SP1)
Windows XP Professional with Service Pack 3