Communication Ports

Hi,
I have a windows nt4.0 server w/a internal modem on com3 port. When I go in the control panel under ports I see I have com1-com3.On the outside of the server I have 2 com ports. I tried hooking a device on to one of the external ports, and that worked fine. But that stopped my internal modem from working. I tried the other external port w/the same problem. I guess my question is how can I get the other device I’m hooking up to work on a different com port. The device I’m hooking up works fine on com1. Not sure how to get the device on to com 2.. Any help would be a plus….Hope this makes sense.