I can now confirm that the Windows Vista MSDN x86 ISO is fully installable using Virtual PC 2007 Beta on Windows Vista Ultimate 64bit.
Even though these are both MSDN images, neither of them was activated, nor did I enter a serial number during the install. Just click next when they ask you for a serial, and make sure to confirm that you do not wish to enter a serial number by pressing the “no” button.
(click on thumbnails for 1600×1200 images – the virtual machine is running at 1280×1024)
The installation took some time, even with 1GB of RAM allocated to the Virtual PC 2007 virtual machine, but after about
30 90 minutes or so, Vista Ultimate x86 virtualized on Vista Ultimate x64 using Virtual PC 2007 is a definite go-ahead-and-try-it install.
Follow normal VPC installation procedure, select Vista as the guest operating system, and chug along as the install proceeds.
Coming up next: full installation instructions.
Note: Unfortunately Virtual PC 2007 is beta, and I don’t see any plans for adding 64bit virtualization any time soon. If you have info that states otherwise, please let me know is this appears to be the only viable option for Vista VMs at the moment.