Setup a M0n0wall router with two NICs (WAN & LAN), 10MB full-duplex WAN 
connection.

Is it possible to add a third NIC that will simply mirror traffic to a 
second card in another box that would be running nTop for monitoring? 
Would like to monitor either the WAN or LAN (WAN preferably, but either 
would suffice).

Was thinking this would be far cheaper than getting a managed switch for 
the same purpose :-)

- Shaun