Have you tried using VMware Converter to convert the VPC image into a VMware image? That would allow you run your W2K environment directly under Fusion.
Converter is a free download. Although it has both a paid and a free license mode, I believe that converting Virtual PC images is among the things you can do in its free mode (so-called "Starter Edition"). (Caveat: I've never done it myself, and I have no VPC images here to test with.)
http://www.vmware.com/download/converter/
Converter is a Windows-only tool, so you will want to run it inside your XP VM. After you start it, launch the "Import Machine" wizard, tell it you want to import a "Standalone virtual machine, backup, or disk image", and then point it at the VPC VM's .vmc file.
Unfortunately, Converter's current version (3.0.1) can only emit Workstation 5 VMs, which are a little behind Fusion VMs. But they'll run just fine under Fusion, just without some of its more advanced features--which, for Windows 2000, you probably don't care about anyway.
If you want to make a real live Fusion VM, use Fusion's New Virtual Machine wizard, and, when prompted for a virtual disk size, instead choose the advanced option of pointing at an existing virtual disk: the one Converter wrote for you.
