You might be interested in the equipment I use for geocaching. Its basically just my HTC cell phone with Windows Mobile for pocket PC 2005. As GPS/map software Pathaway, which is actually a Shareware, is very helpful. PAthaway costs about 59 bugs and has a lot of funcationality starting from compass view up to showing detailed topo maps, tracking, waypoint database, alerting if you go away from your destination and many many more. Just have a look at: www.pathaway.com. This money is a very good investment, but It will take you a while until you are able to use all functions. As GPS receiver I personally use an BT NaviLock BT338 Bluetooth dongle with SirfStar III chipset, which connects to the mobile phone. More you really don’t need to start your geocaching day.
The navilock GPS receiver: