I searched to see if this was addressed, I have found a solution.
I have abbreviated the instructions, but will go into detail if this has NOT already been solved by someone else.
1) Install and set up a "serial to ethernet connector" such as Etimas - http://www.eltima.com/products/serial-over-ethernet/
2) Open firewall ports to allow incoming access to the port you chose during s2e setup
3) Start up and select Null Modem multiplayer game.
Works like a charm, been playin since yesterday. Might work for other c&c games.