public server can't login into privite d

We have a Cisco router with 2 NICs. One for the private network and the other for the public web side. I am having a problem adding a new server to the public side. I already have my exchange server there and I can log onto my private network from it. I have a NT 4 workstation and I plugged it into the public hub and it logs in. I took the hard drive out to add a larger (20 GB) drive and installed NT 4 server with IIS. I did put on the hosts file, cleared the WINS data base, aded the computer to the domain from the PDC. But the NT server won't see the domain. Any ideas??