A multiplatform tool
One of the things I like the most about the Arduino software is that it is truly multiplatform, which means that it is exactly the same environment whether you run it under OS X, Windows, or Linux. You could find some differences in the installation process of every operating system and differences to get it up and running, but once you have it up and running, it is just the same in any platform.
So, let's go ahead and present to you the whole process to make it run under the operating system of your choice.