Not through the expansion slot. I have a dozen or so Palms and most of the time I've just used a serial cable from the Palm to whatever flavor GPS I had at the time. I've got Solus Pro from Delorme on it, and have used other mapping software to do it. Works OK, but you still have the GPS, cable, Palm thing going on.

Depending on your needs, I would just get a standard eTrex, build your own data cable (save your ~$40 for something else, all you need is ground, data in and data out) and you can basically hook it to anything that has a com port. This way I use my eTrex with my laptop, desktop (I have a GPS repeater above my head here at work), Palm, and for a standalone unit. This way I have my car navigation, playing at work, mapping availablity in the wild (using Palm) and map/compass companion with one unit.

--Chris