FWIW: I have successfully copied the xp virtual drive by just copying the .vhd to another directory and then
go to virtual pc and creating a new machine. Telling the system that I will use a vhd already created. It then creates the ancillary files necessary to use and modify the new virtual xp.
but then I run windows 3.11, 2000, 98 and xp all under virtual PC..
I always copy the .vhd files off to an external drive as a sort of warm fuzzy.