I'm trying to represent webcam data in an LED matrix [wall], and i'm wondering whether PD [or PDuino] is the tool for the job.

An example is someone stands infront of the webcam and on the LED wall their sihlotte is shown.

Is PD a good tool to investigate for this?

oh, and i'm using an Arduino Duemilanove and a Arduino Mega.

Any help or tips are greatly appreciated!

Sure. Check out GEM. Specifically pix_video for the webcam and pix_data to scan the pixels for values which you can then apply to your matrix. I would skip the pduino firmware and send bytes over serial to update the display... If you have an 8x8 single color matrix, that is an eight byte message (8bitsx8bytes), if you aren't using pwm. Should be pretty easy to set up using comport. Things get complicated if you want dimming; each LED will need a byte, and you'll need to mux the PWN outputs. Alternatively, you could do this without a computer, using a serially attached camera and only the arduino. That would probably be even easier.