this configuration seems to work for me in case anyone is wondering
about getting another ethernet interface via USB on an net4801.
i picked up an SMC2202 EZ Connect USB adapter (ebay for ~$10) because
someone metioned that in the past as possibly working with m0n0wall.
it detects when hot plugged into the USB connector and also on boot as:
"kernel: aue0: SMC, Inc EZ USB/Ethernet Converter, rev 1.10/1.01, addr 2"
and everything works as a normal interface.