2 NIC on NT Server & HW Proxy

I have a decision to make. I have an old 2baseT (BNC, 50 ohm coax) TCP/IP NT 4.0 network. It works fine. I want to install 3Com Off.Connect 3C891 Proxy/Hub/ISDN card – has no BNC connector! I shall install a second NIC with RJ45/10BaseT/UTP5 and connect it to the 3Com Off.Con.
I’m looking for the safest and cheapest solution!
To have two NIC’s on the NT 4.0 server working together I’ll assign different IP address and enable routing. What about net browsing?, what about priorities and bindings?
Is there anything else I should do to have people on existing network reach internet via 3Com Proxy?