Play Halo 1 just like the old days on your original Xbox
HaloMD (Mini Demo) is a free and legal download that extends the life of Halo (for Mac users). If you have an Xbox 360 controller, it's just like you remembered when you were hopped up on Mountain Dew LiveWire playing LAN direct connect CTF on Blood Gulch with your High School buddies. And it's still just as freakin' fun too!
Download the Goods
Go to HaloMD.net to download the game, and if you have a 360 controller grab the TattieBogle Xbox360Controller drivers to allow you to use it. Make sure you use the "Controller" profile when mapping your buttons. You can configure your buttons exactly how they should be set by using this Microsoft Support page as a guide.
Tweaking your Controller Settings
I also recommend setting your Xbox 360 Controller joystick settings to have a slight threshold. For some reason my controller's joysticks are a little shifty, so I set about a 20% 'give' on both sticks. You can get to these settings by going to / System Preferences / Xbox 360 Controllers.