Connections with a Proxy Server

I am using MS Proxy2 and am trying to set it up with 2 NIC Cards to act as a firewall. I use WINS to connect with a remote Exchange server. I have the Proxy server set up so the
outbound card is plugged into a router I do not control and the inbound card is plugged into a hub. I can get out onto the internet but I cannot see the remote winserver or exchange server. The outbound card has a gateway and the internal card does not.
HELP