I’ve been playing about with the Arduino the last few weeks. It hooks up through the computer’s usb port and can be used to take in signals from buttons, sliders, dials, sensors or whatever and can also control devices connected to it from the pc.
It can also act as a standalone device and can be programmed… so for instance you could have a microphone as an input device, have a lamp connected to the output and then program the chip so that the lamp switches on when you clap your hands.
The pdf book from www.arduino.cc provides a great introduction to how it works, including how to build your own ‘Virtual Etch-A-Sketch’. I’ve managed to make a heat sensor control an interactive piece built in macromedia director, so quite pleased with that!