If I repeat info I apologize...

I was following Mac/Garmin for a bit and then got side tracked w/ a huge house lifting project.

Went back to the Garmin site and found all this support for the Mac:

Garmin and the Mac

"Garmin is committed to creating a great software experience for all of our customers.
This page is dedicated to keeping you up-to-date on our growing range of software
made for Mac and helping you enjoy the full potential of your Garmin device."

I was finally able to update the firmware and maps on the BMW Navigator III.

They also have some neat little "apps" for the Mac.
Well worth the time to look around.

Finally a 'native' updater.