Hi Colin,
Start Osm2Garmin and start processing. Osm2garmin should start downloading of planet-141203. When torrent download starts and at least one piece is downloaded, stop processing and finish Osm2garmin. Replace planet-141203.pbf in the Osm2Garmin working directory with your downloaded file. Both files should be exactly the same size. Run Osm2garmin. The software will check the provided Planet file and continue processing.
Please note that externally downloaded version MUST be the same as the version Osm2Garmin started downloading. Osm2Garmin always downloads the most recent Planet file and it is not possible to change it.
Hope it helps.
Frantisek