You cant create a Win7 VHD from XP. Completely different OS's. Unless your asking how you can still use XP and use EasyBCD to boot to a VHD. Again cant. EasyBCD is create for use with Vista/Win7, NOT XP. XP doesnt use the BCD to boot and there for what your trying wont work.
If your trying to create a VHD of Win7, yes it is possible from within Virtual PC.
Linux VHD is out there. Just have to find one that works for you.