Honza,
I ran into the same issue trying to import the XP Mode VPC (vmware converter not configured). I ended up making it work by doing the following:
Run VMWare VCenter Converter Standalone,
Choose Convert Machine button in upper left corner
Select Type: Backup Image or Third-Party Virtual Machine
Browse to the location of the vmc file (in Windows 7 path to my file was C:\Users\USERNAME\AppData\Local\Microsoft\Windows Virtual PC\Virtual Machines)
Configure Destination System settings (Destination Type: VMWare Workstation or other VMWare virtual machine, Select Vmware Product: Vmware Player 4.0.x, Choose name of VM and choose path to new VM)
Once the conversion process was complete I opened VMPlayer and chose Open Virtual Machine and pointed to the new VMX file in the path configured in the conversion process.
Power on VM and ready to go.
Hope this helps,
Tyke