Garmin Etrex and HP hx2490B PPC

I am currently trying to make my hx2490b with a Garmin eTrex GPS. I connect
the RS232 connector of my GPS, through a null modem adaptor and an HP
FA122A#AC3 Serial cable connected to my 2490b. I have set latter's baud rate
at 4800, which matches my GPS NMEA 4800 setting. I have Pocket Street 02
maps on it, but the program just says "initializing GPS" for a long time and
nothing happens.
I would be interested to know what should be my "GPS program port" and "GPS
hardware port" settings on the PPC...
TIA