While the HP is one of the better PDA's out there (if not the best), using a Windows based operating system, the Palm system is much cheaper and can do practically everything the HP's can, only slower and less of it. You'll get more battery life out of the cheaper units as well.
Having used both, I prefer the Handspring (the original designers of the Palm Pilot broke off and formed another company) to the Palm Pilot. I find the screen easier to write on. You can get programs ("Documents To Go" the most popular, downloadable at www.cnet.com in the PDA section) that will allow you to run and modify Excel and Word programs with ease, as well as pda documents (though they eat up alot of memory).
I wouldn't go to far without my Palm Pilot flying EMS. You'll often find yourself away from base being rerouted, and you can flight plan, make all sorts of fuel/weight calculations, having all your waypoints and contact information, aircraft performance information, limitation notes, moon phases, tide schdules, sunrise/set, alarm clocks, pics of the wife and kids..... you are only limited by your imagination. If you get an internet capable unit, you can download all the weather you could ever want from navcanada, write emails or surf.
Once you start using one, it quickly becomes an invaluable aid.