Portal 2 not loading! I need some tech savvy people to help me out, reddit.

I just bought Portal 2 from the Steam sales and I tried to play it for the first time. The Valve logo screen came up fine and then it showed a picture of the menu screen, but without any options. Then it just crashed straight to the desktop. I checked the integrity of the game cache and all the files were fine.

I am on a Mac 10.5, which Portal 2 doesn't support, so I am trying to use Crossover Games to run steam. This works for me for other games like Oblivion, so I hope it's not the problem. My graphics card is Nvidia GeForce 9400.

Any advice you have is welcome!