Can I use an HD capture card?

Yes you can, but, you will need the HDMI cables for your Xbox. (Red, blue, green etc. etc.) On their website, which will be sourced below, they have separate programs I believe just for Mac. I too have a Mac, but I have a MacBook Pro, and even though I use my PC to record, I can always use my Mac to record my 360 game play. By the way, my PC stinks so you can surely use a Mac for it.