NT Server will not detect Linux Gateway

I am running a Windows NT 4.0 client/server environment with a Linux Box Gateway to the interenet. I also have a second domain with a lone Windows 2000 Server. I had no problem getting my workstations (both NT 4.0 and 98) to detect the internet through the Linux box using IP 192.168.0.100 port 80. However, I can’t get my NT 4.0 or 2000 server to detect the proxy even if I give it the IP and Port to look for. Any suggestions??