Try reading the "Google Earth Tracking" thread in the Mac forum. I think you'll find what you need there.
I just bought a intel mac mini as my car pc, itl be here tomorrow. I am faced with deciding what operating system to use. The more I read up it seems that there just isnt as many gps options for OSX also I dont think there is any real time gps tracking in google earth with OSX, or Goops or hacking kml files. Anybody have some input on it?