i have something called "Virtual Server" that lets me set ports that come into the router forward to this PC.
Then i have this "Special Applications" here is what the help for it says.
"Some applications require multiple connections, such as Internet games, video conferencing, Internet telephony, etc. Because of the firewall function, these applications cannot work with a pure NAT router. The Special Applications feature allows some of these applications to work with your Barricade. "
I have a SMC (
http://www.smc.com/) Barricade 4 port 10/100 mbps router (port means 4 Computers able to be connected to it for those who may not know)