Here are the steps I used to work with Processing using Eclipse. Eclipse is one of the best, all-purpose (C, C++, Java, PHP, HTML, etc), open-source, and "free" IDEs available.
- Install Eclipse (minimally, Java IDE) from here: http://www.eclipse.org/downloads/
Install Proclipse from here: http://code.google.com/p/proclipsing/
Be sure to follow the install instructions here: http://code.google.com/p/proclipsing/wi ... ingStarted
Code completion on the Mac won't work unless you configure the Keyboard properly: http://stefaanlippens.net/code_completi ... clipse_osx