Its been a while since I dabbled with processing.py, but it seems like it might get interesting again soon as Jonathan has started updating it to processing-2.0. I think Ben Fry has the idea he would like to create a mode for processing.py in the processing ide in the meantime you could try the tools I created to run processing.py from jEdit here. Jonathan is rather fond it seems of using spaces in folder names ( and file names, and other illegal characters how do you cope with that?) so for a while it defeated me, however, as I just did for vanilla processing I have updated my jEdit commando file to cope with spaces ( I wish they wouldn't do that damn Microsoft all over again).  Here's an snapshot showing use of exuberant ctags with a processing.py sketch. Not shown is you can also get get code completion if you wish.

I have just made my updated jEdit tools for processing.py available at github. This now includes a set of "abbrevs" for coding in processing.py (based on the vanilla processing set, translated for python syntax, which are also include in abbrevs file). In addition I have published quite a number of worked examples to get you going with processing.py. I have also started a blog to chart my experiments with processing.py (for processing version 2.0) here. Now is good time to grab jEdit as version 5.0 has only just been released.