Struggling with SD card read on Arduino
I recommend you get a MicroSD card breakout board from that link, or something similar. That's around $US 15.



That includes the logic level converters. That particular board is for the **micro* SD card, but similar converters could no doubt be found for an SD card. Or use that one with a micro-SD card and just get an SD converter for when you plug it into the Mac.

I personally have used the SDfat library without any problems. However since he started rewriting it, I did have some issues. I have a backup of an earlier version which might be useful if the live library doesn't work for you.

You might be best off not formatting the card, but leave it as factory formatted. That will probably be compatible with the Mac, and also the SDfat library.