After a bit of research it appears your biggest issue, assuming you have just plugged in and hoped for the best, is that (naturally) mac does not have the drivers to understand an Xbox controller.
A good rule of thumb: If you plug anything Microsoft into anything Apple and just hope for the best, your going to have a bad time. They just don't like talking to each other.
These two sites gave me a bit of insight into connecting various original and third-party controllers. I assume if you follow the driver installation you have a good chance of that fixing everything, just remember that the driver is what the computer uses to understand the device. It is possible that a different driver will interpret the controller a little differently - this may go as far as swapping buttons on the player.
That said, the driver refereed to at jacobtomlinson.com (provided by tattiebogle.net) has come up in a few times in the past, so I would assume that is the general driver players would be using.
Also keep in mind that the drivers impact the identification of the buttons themselves, so you can not use native windows reference to the controller and expect the buttons to remain the same. This last link shows the button references on a Windows system, and the reference system used by the tattieboggle driver.