In the virtual PC console, click NEW, and follow the wizard as you would to install any other kind of system. Pick "Create a virtual machine", go on and give it a name, and under "Operating System" select "Other". Now in the RAM and Virtual Hard Disk settings, specify suitable values for your "Other" guest OS.
See the list in the first section of what devices are emulated for a list of the drivers you need to have available for your Linux install. Remember, you need to install drivers for the emulated hardware, not your real hardware. Given that emulated hardware is usually a bit behind the curve of modern physical hardware you might actually find this isn't too difficult to do. Once sourced, drivers install in the virtual machine the same way they would on a physical one.
Job Done.
I never used Virtual PC just found that on his webpage... here at the bottom