2 PCs on network playing COD2 online

Hey everyone,

I have a Linksys Wireless router (not sure what the model is-- W54 something or other... the really common one). I have 2 computers hardwired to it using 6Mbps cable connection and we play COD2 online. I'm having problem trying to get both computers to play in the same server at the same time. About 50% of the time it works like a charm, but sometimes if one of us is already in a server and the other joins, it kicks the one who was already there.

Sometimes this happens and both get kicked-- sometimes it doesn't happen at all. Honestly, the weird part is that it will go a week and never happen at all. It only happens when we are on the same server. Apparently the server (whichever one we happen to be on at the time) sees us as having the same IP address because we are both behind the same router. I've tried doing something where I add +set_netport 28961 or something to the shortcut on my desktop and that didn't seem to help any.

Both computers are running Windows XP with all updated drivers, etc. and the router firmware is the latest version. Any help would be appreciated