(I'll upload some photos of this tonight)
Step 1: The parts I started with
(note: at the time of purchase, I didn't know it could work with my handheld GPS)
The ETrex GPS - really cheap haldheld unit that has served well over the last couple of years.
DB9 Serial Connector - from an old computer. You should be able to find this at your local electronics shack.
Step 2: Figure out if it can work
A google search for NMEA and ETrex shows a site listing GPS units that support the standard. Mine is listed, woohoo.
I later discovered that in the setup menu in the GPS, its a communication option (I should have checked the device first).
Step 3: Wire things up
It shows serial communication from pin 2 or 3 and the ground on pin 5.
I fire up the radio and the GPS.
I just stick the bare ground in the number 5 hole in the serial connector, and the other wire in the pin 2, nothing happens. Move it to pin three, a few seconds later, life. Woohoo.