Well if you want to use your PDA for a GPS receiver then this is probably your best bet:
GlobalSat SDIO-502 GPS Receiver. If you hadn't purchased your Dell already a better option might have been one of the Garmin PDA units with built-in GPS, but you probably got a good deal on the Dell so no problem with that. As far as software goes, if you are primarily using it for road navigation then MS Streets and Trips has a version for PocketPC that comes with the desktop version, and Delorme has one as well (can't remember if you have to purchase it separately or not). Theres a lot of other options available that I don't have direct experience with but you can find it using google.