This may be for the ASUS board or network board, ... anyway
You can use the second connection
1. For single computer internet sharing. E.g. just hook up a laptop using a cable to the second nic socket for internet access, assuming the first one already has an existing network and internet connection.
2. For multiple computer access as a router, assuming the first one has an existing network access, the second connection can then connect to an external ethernet switch, and more than one computers can then be connected to that switch for network and internet sharing (as a new sub-net).
In additon, it requires the usual sharing and router setup. It is required to set up internet sharing on the first connection as a subnet gateway and a DCHP server. And the second connection as a DCHP client in a subnet of the first one.
A regular non cross-over cable will work w/ the 3COM nic even for computer to computer connection (I found this secret) , but a cross-over cable is needed for the nforce2 nic if used as the 2nd connection for computer to computer connection.