[Twisted-Python] specifying the site and port to a twisted web server

I have written a highly simplified twisted web server using twisted extending one of the demos, but I have one small problem. I cannot see out how to arrange to have the server listen one particluar address:port combination. The system I want to use it on has a pair of NICs and I need the server to listen on one NIC and not the other due to port conflicts. Any help would be appreciated.