I use Symantec Ghost (http://www.symantec.com/sabu/ghost/) to create images of physical machines usually over the network. You can create a boot floppy to run inside of Virtual PC / Virtual Server. Symantec provide a nice wizard to do this with - but unfortunately they do not include the driver for the Virtual PC emulated network card.
The driver that you need is the NDIS2 Unified DC21x4 driver from here:
Once you have downloaded this package you will want to point the Symantec Ghost boot floppy wizard at the 'mslanman.dos\drivers\ethernet\dc21x4\dc21x4.dos' file. You should not need to specify any special parameters for this driver in order to get it to work.