Assuming a 9 way plug, wire signal to pin 2 (rx), common to pin 5 (sig ground), set up your serial port correctly and hope for the best.

Oh, and if you must post hardware questions, mark them OT or ask them in the CB (this is waaay off topic - hopefully you will soon be using perl to talk to your device, but at the moment it looks very much like a hardware question) ;-)

Update:this might come in handy