For Fall 2012 we will be learning to code interactive works in the patch-based program Quartz Composer. After gaining a sense of comfort in that environment, we will move to the more complex (and flexible) program Processing.
Quartz Composer can be downloaded for free from developer.apple.com
Currently, the version available on apple's site seems to only run on OSX 10.7 and 10.8
If you are running earlier versions of OSX, you may need to download a program called XCODE 3.2.1 and see if QC is packaged with that program.
If you want to get started in Processing, you can download it for free as well (cross-platform and open-source).
We are currently running/learning and using Processing version 1.5.1
Pretty soon we may migrate to the large upgrade of 2.0 (after it comes out of alpha version).
Download processing from processing.org
Also check out: processing.org/reference to see available coding terms.