if you still have problems another way is to use a program called dxport from
www.puffinsoft.com this has worked for others in the past for playing ta from same ip.
here are some excerpts from their site...
DXport is an app that will let multiple people play most games that use the Directplay network code 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. What DXport does is force DirectX to the ports you specify.