I have been using my 760 with a Mac for quite a while and have not experienced the problem you described. I have however, not "upgraded" to Snow Leopard out of fear many applications would no longer work. I suspect that is the issue you are having. Were you having that problem prior to Snow Leopard?
I don't know if it would have worked under a prior version of Mac OS because I had already upgraded to Snow Leopard several weeks before I bought my Garmin. I'm still finding out stuff about the Garmin and I'm hoping that I at least get the voice and/or beep warnings of speed cameras etc. I think I can test that with a simulation.
I certainly won't be buying a PC any time soon! I could run Windows on my Mac, but I think I read that the Garmin isn't recognised on USB under that scenario.