In order to convert virtual machines from one program to another (in this case from Virtual PC to Microsoft Virtual Server, i.e. vmc to vhd conversion), you will need to convert all files as a bundle and not just few files. It is true that the wizards used for conversion usually let you pick one file with settings (like .vmc), but you will also need all of the remaining files for a successful conversion of whole virtual machine.
Open VMC file Open VHD fileA application used to run virtual computers on one workstation