It wasn't so good there at one time.
I assume you have the Garmin ANT Agent or the Garmin Communicator Plug-in installed.
Give them a call.
I have used my gps on my g4 tower. I had to first get it recognized on a pc but then it worked on the g4. Now I have an imac 27 inch i7 and the garmin nuvi 850 is not recognized though it shows it is connected on the garmin screen. Any suggestions?