Routing issues

I am trying to set up a remote office to communicate with our main office. The connection between the two offices are handled via ISDN Lan Modems. I have a multihomed BDC (NT 4.0) that I have enabled IP Forwarding and installed the RIP service on. The member server at the remote location is W2K. The two modems communicate with each other, and I can ping one nic in the BDC, but I can’t seem to get past that point. Any suggestions will be appreciated.