Ok the instructions that come with the Garmin forerunner are completely wrong, the CD is useless (it has the manual but no software) and the Garmin support website is not much help either. There are all sorts of discussions on the Garmin site for Mac users about ‘it does work with Lion’, ‘it doesn’t work with Lion’ and so on. At one point it even had me downloading a PC .exe file!
The answer is that it does work very well with OSX but there are two separate pieces of software that need to be installed.
1. The first piece of software is a Safari/Firefox/Chrome Plugin that lets your browser talk to your Garmin. You can download it from garmin.com under ‘Support’ menu then ‘Software’ then ‘Software for Mac OS’ then ‘Garmin Communicator Plugin‘.
When it’s downloaded you can test it on this test page: http://www8.garmin.com/products/communicator/test/
2. The second piece of software is a USB driver that talks to the Antenna. Again, you get it from ‘Support’ menu then ‘Software’ then ‘Software for Mac OS’ then ‘Garmin ANT Agent’. When it’s downloaded you can ‘pair’ with your Garmin device as per the instructions.
Finally if you want you can go to the mac app store and download the Garmin fitness software for free.