I'm carrying out a similar project, using a combined GPS/CDPD unit that plugs into the empeg's serial port. (CDPD gets me a 19.2Kbps wireless Internet connection.)

In this case the GPS protocol is a simple UDP exchange, but I get the same information Kim mentioned.

What would really be nice is to get an empeg<->Palm protocol going so we can do things like external maps, playlist management, and IP tunneling so passengers have something with which to amuse themselves besides watching visuals.

Hmm, this is getting off-topic.
-v