Just spent a few hours getting the SP2820 to work with my Mac. Garmin does not make it easy to be a law abiding customer. (And again, I gave up... As my SP is previously registered on an account they no longer acknowledges, it seems I cannot buy upgraded maps.)
You need to install 4 sw packages, all available for free on Garmin´s website:
- BaseCamp (this is "the new MapSource")
- MapManager
- MapInstall
- POI Loader
Should be smooth from here, if you don´t get slapped by their copy protection scheme. But a quick google search should lead you to the relevant torrent.