If you have an external power source plugged into the Arduino, you might be overloading the voltage regulator by drawing too much current through the +5V line.  If you have 5*16 LEDs, this is 1.6A! of current.  You could try powering all the LEDs from the external power supply directly: hook the positive legs of the LEDs to the "VIN" pin on the Arduino.

To use multiple TLCs in series, hook SOUT (pin 17) of the first TLC to the SIN (pin 26) of the next TLC, and so on.  Try downloading the latest library (TLC5940LEDv006.zip at this point).  Then run the examples, but change the #define NUM_TLCS at the top to however many TLC's you have daisy chained.

I would organize myself but I'm afraid I don't have enough time.  I'll ask around.

I would be up for a workshop / hackfest.  I'm an EE / CSE student at UW and I think there would be a lot of interest from undergrads who want to get into microcontrollers.  Also, the DXArts (digital arts) department uses Arduino for all their mechatronic art/courses, so we may be able to get some experienced people to give talks.

Very cool!  Nice instructable too.

I made a keyless entry system with an Arduino, servo, and a capacitive touch sensor.  Touching a wire on the outside of the door with the right pattern turns the door knob on the inside (this opens the door if it's locked from the outside).

The project page with more info:
Keyless Entry System Using the Arduino

The Youtube video: