I had to find a way to control a 32*32 led panel at a decent framerate. Unfortunately, the arduino theoretical limit was 7fps.. So I decided to use a teensy! Much more powerful, especially for serial-intensive task.
I came across Markus Lipp work, who just achieved that. Unfortunately, I couldn't figure out how to make his java app work.. So I adapted it to make it work with processing and it works just fine!
Basically, you need to download this bundle, wire the teensy according to what is written in the .ino file. Then, to test the wiring, run the test sketch (which displays a colour gradient).
All set? Then run the client sketch on the teensy, run the processing app and the panel will display the webcam flux! Easy! And if you want to display images or a video file, only a little modification in the processing file is needed...