For street driving you may use a receiver in conjuction with a notebook - though you might want another person to hold it for you or the noteboook will drop, bang and crack sooner or later.
For outdoors the unit must self contained thus you must be able to upload maps to the GPS unit. Only the OEM's mapping software can upload maps. If you have a Garmin, mapsource is the only choice, or you have a Magellan then mapsend only. All other 3rd party software via comm port/NMEA can transfer position, waypoints, routes only. You cannot upload map to the GPS. Then means you must use the GPS together with the device that the software runs on.
It appears you guys are interested in street driving. you probably should get something like a palm with Magellan receiver or Garmin Ique. Handling a notebook while you are driving is unmanageable.
All maps other than Magallan mapsend are quite accurate.