Greetings,
I have an HP Compaq 5555 with the NavMan add-on GPS sleeve and software. I find this unit Great for driving in the car or taking on a road trip. For geocaching the software can work, but it's VERY basic and can lead to alot of walking around. I purchased CacheDragon software for the IPAQ specifically for geocachine, and it works pretty good. It has more of the features you would expect for geocaching, including breadcrumb trails. It also stores and reads downloaded data from geocaching.com very nicely. I REALLY like being able to read other people's visit logs to a cache, and sometimes the hints, while out searching.
It's not perfect by any means, but seems to be a good addition to help you out.
My only problem with caching with the PPC is keeping it dry. The unit is expensive and not built well for the outdoors....