Topo/NZ supports Garmin units for upload/download of waypoints and tracks.
You can also use Garmin protocol for real-time tracking of your position on the map. Note that some navigation GPS units, like the Palm-based iQue are not supported. Other units, like the Oregon, require a special Garmin USB cable for realtime tracking.
NMEA protocol is supported for or real-time tracking of your position on the map.