VirtualBox natively supports VHD format, so stop shaving those yaks.
Where is that $300 coming from? You run VirtualBox on your computer (free), install free VHD's (free), and free the free free with your free free (free).
Sure you can run the VHD in VirtualBox. Then you run into driver problems (the VM drivers are set up for VirtualPC) and activation problems (see comment on other thread). And you get to do everything again in three months and hope nothing else has changed.
Where is that $300 coming from? You run VirtualBox on your computer (free), install free VHD's (free), and free the free free with your free free (free).