After buying my Palm T|X I wanted to use it for GPS my self so I bought a Holux GPSslim240 Bluetooth GPS Receiver since it was small and fits in your pocket really easy and If i remember correctly has an 8 hour charge on its batt before needing to be charged (course in your car you can charge it and just run off the batt) I use TomTom 6.030 for City driving and I've found that GeoNiche is good software to use for finding caches which might be of interest for you.
Well I don't know if any of that helps but hehe at least its something to look into.