AAXD,
PocketPC's or Palm PDA's are a lot of fun with GPS systems. Here are some ideas for your future PDA/PocketPC.
HP makes really good PocketPC's called the iPaq. Current new models are the hx2000 series types. The top of the range unit has lots of internal memory, fastest CPU, biometric finger reader, but no VGA screen.
Dell makes great also great PocketPC's, called Axim. Their top range model is a unit with a VGA screen.
VGA screens are great, but consume more power and are slower in update time, compared to traditional PocketPC screens of 320x240 (QVGA).
All top range units come equipped with Wifi (Wireless Ethernet interface) and Bluetooth.
Check out ideas at
www.ipaqhq.com and
www.aximsite.com where you can browse the forums.
Probably most GPS mapping software manufacturers offer aviation maps. I know this for the company who's product I use.
www.Teletype.com.
Your current GPS, you may have to get a serial cable for the PocketPC that you ultimately buy. Check the Navigation software manufacturers websites for GPS compatibility charts before you buy their software and/or hardware. Not required if you use a Bluetooth enable configuration -> no messy cables.
Lastly, typically PocketPC's do not have USB ports. There are SD cards with USB ports on them that you may interface to.
Hope it helps.