It is hard to buy a laptop today with a 9 pin serial (COM) port as most of the new models only come with USB (Universal Serial Bus) ports.
The USB to serial converters have improved over the last few years and are now mostly quite reliable for GPS and other applications.
On Just Imagine we use inexpensive ($30) Keyspan USB to Serial converters that are readily available and so far have had good results. There are several other choices and prices available.
The GPS NMEA cable connects to pins 2 and 5 of the 9 pin connector. Look for the tiny numbers (1-9) on the connector.
Pin 5 is the ground connection and pin 2 is the NMEA signal coming from the GPS.
If your laptop software can upload waypoints to the GPS device, then you need to connect pin 3 as well, which is the NMEA signal from the laptop to the GPS.Howard [ Just Imagine ] 10-Mar-2008