You don't. A Macintosh is a great computer, don't get me wrong. I own one. I use it for all my multimedia and design work for school but I don't game on it. I have no games on my Macintosh unless it has some default ones in which I greatly doubt. Macs are not gaming computers. They do not hold the capacity to support video games. If you have a Mac, there isn't much point using it for games. No source engine game will run on Macintosh to my belief. This includes Half Life 2, Portal, Team Fortress 2 and Counter Strike: Source.