HOWTO Convert geocaching gpx files to TomTom Points of Interest (POI)

Use gpsbabel:

gpsbabel -i gpx -f 1483978.gpx -o tomtom -F Geocaching.ov2

Dump it in the maps directory on your TomTom with a Geocaching.bmp icon (mine is on the left). I use the 720 which comes pre-loaded with maps. You can mount the device's memory itself and find the maps directory in there.