When downloading Garmin Express to a Mac that does not meet the applications minimum requirements, the message "Garmin Express is not compatible with your operating system" is displayed.
The Garmin Map Updater application can be used as an alternative to update the maps on compatible Garmin GPS devices. High Speed Internet access is required. Not for use with dial-up, satellite or Mobile Broadband Internet access.
Garmin Map Updater for Mac OS X 10.5.8 users:http://download.garmin.com/lmu/GarminMapUpdater.dmg