I recommend that you do not copy the machine settings (*
.vmc), only the harddisk image (*
.vhd). Then simply create a new virtual machine with a different name, but instead of creating a new harddisk, attach the existing/copied hardisk file.
BTW: copying virtual harddisks can result in some problems if more than one copy is started at the same time (especially in a company environment, in a windows domain). As far as I know, this is because all copies of the PC will have the same SID (Security ID, which identifies the PC).
If you plan to use the virtual PC in such an environment, I suggest you use SysPrep to create a harddisk image that can be copied without problems. Or at least use the NewSID utility to create a new SID on each copy.