Domain Trust Between Networks

We are trying to set up a domain trust between two networks. One of the networks has a firewall, the other does not. I have opened up ports 135-139 on the firewall for both networks. We are not using WINS but are trying to use an LMHosts file. Is it necessary to use WINS? Is DNS involved? I can ping between the two networks and I can see the server using the IP address. Help!!