Call of Duty Mp On Two Systems On Single Connection


I just bought a second copy of Call of Duty with the United Offensive expansion pack, updated everything to the latest version, and tried to have two of us playing in the same network game at the same time. However, once one of us enters an online game the other can't see it in the list of servers and if we try to do it at the same time one of us simply stops during the game map load process. All of ther network functions are working fine. How can I get two Macs on a single hi-speed cable connection to play the same online game in Call of Duty?