First get a route on the map using "Get Directions". Then use "Get GPX" to download a GPX file for GPS navigation. Note: business names will not work for GPX; use a street address or lat,long position
TRK (track) format will work as a route in Maemo Mapper. RTE (route) format will work as a route for some Garmin GPS sets via MapSource software.
The GPX conversion service http://gpx.geotags.com/cgi-bin/gpx.cgi?saddr=%s&daddr=%s should work for live route downloads in Maemo Mapper.
See also this page to find lat/long from a map or street address