I'm not a Mac person myself, but Mac-enabled user LightningJeff posted these instructions:
[You] need to have MapManager and MapInstall installed on your Mac. These are Garmin programs and are required in order to install maps on a Garmin GPS receiver. So get them: http://www8.garmin.com/support/collection.jsp?product=999-99999-06
(one download for both items).
Once you have those installed, the process is really this easy:
- Click the link for the mapset you want and save it on your computer.
- Double-click the downloaded .tgz file; this will unpack it to a single .gmapi file.
- Double-click that. MapManager will prompt you to confirm that you want to install this mapset on your computer (for use, for instance, in BaseCamp, and necessary for installation to the GPS receiver). Confirm by clicking "Install." When that completes, click Quit. You can now delete the .tgz and .gmapi files.
- Connect your GPS receiver. It should show up in the Finder.
- Open MapInstall. When it detects your receiver, select the mapset you want to install from the popup; then select as much or as little of the geographic coverage as you want to install on your receiver; and let 'er rip.
When you are making the selection of tiles (geographic coverage) in that final step, just back sure that you are not selecting the "Detailed Background" tile.