Recently bought Route Planner Millenium (Palmtop Software). This is EPOC based but useable on Win CE machines as well, apparently. There is a chapter in the handbook 'Attaching a GPS to your EPOC device'.
"To attach a GPS device to your EPOC device, a cable might be provided. If not, you can use the cable that comes with your EPOC device and the PC adapter cable for your GPS device. Additionally, you will need a null modem cable/male-male gender adapter, which is readily available in shops selling electronic equipment."
It further goes on to indicate that the software supports NMEA and SIRF GPS devices. These, apparently, are types of output from the GPS.
I intend to use the program for mapping purposes on the PSION 5 as I don't have a GPS unit ....... yet!