DXport is an app that will let multiple people play most games that use the Directplay network code (mostly Microsoft titles) behind a NAT/Router. Normally you are limited to a single client behind a NAT/Router unless your router supports UPnP. This may also be an option for people that don't like the security issues with UPnP.
DXport allows multiple computers behind a NAT device to connect to Internet games that use the DirectX Netcode.
http://www.puffinsoft.com/
http://www.puffinsoft.com/forum/viewtopic.php?t=243
[ edit ] http://mtm2.com/~bbs/messages/19857.html