I am relatively new to Geocaching (known about it for a while, but just recently started seeking and hiding)... and I already had a PDA. I own a tour company and decided I wanted to test drive a GPS map package that I could rent to clients, so I got the Tom Tom package that Palm is selling (don't get this for geocaching -- it is fine for driving directions, but useless - with an exception or two, see below - for geocaching). It comes with a bluetooth GPSR.
There are a number of software packages out there for GPS and palm, and I tried a few... I am currently using GeoNiche, which is optimized for geocaching. It basically puts a front end on the bluetooth GPS. You can download .loc files (they need to be converted into palm files, but it comes with a java applet that does that for you) and getting them into the palm is as easy as syncing the palm. It does not have a map display, but it is very easy to use and consistently and easily gets me right to a cache. It also loads the descriptions of the caches, which are one button away on the display, and it will decode the hints for you.
As I said, the Tom Tom software is almost useless for geocaching, except for two things. Once, we were geocaching and my girlfriend started to feel ill after a bit of a hike. We found a road, and I loaded the Tom Tom software and bookmarked her position, walked back to the car, and then had it plot a route back to where she was... which was useful because I wasn't familiar with the neighborhood. The other thing that is useful about the package is that it comes with a cigarette lighter cord for both the palm and the receiver, as well as a car mount for the palm.
There may well be better packages/combinations out there, I don't know... my research is limited. But I am really happy with mine... it would work with any bluetooth-enabled palm. Mine is a T-5, but I think the TX might be a better deal these days.