Well, for connecting multiple Arduino's, the easiest way and possibly the best way I believe would be i2c. Look at the examples for the Wire library included with Arduino for ideas on how to use it, here's a link that shows how to talk with 2 Arduino's, I've had 7 working on the same link just to test.
http://absences.sofianaudry.com/en/node/10
Then you would need 1 of the Arduino's connected to the computer, most likely the Master. The Master in I2C controls the flow of data, it tells each chip what to do basically. It's one master and the rest slaves, generally.
You can have multiple masters, but that also adds another level of difficulty. But here's an example that somebody has setup for using multiple masters. (I haven't personally)
There are other protocols available, but will require a bit more hardware as well as software work. I believe you could use SPI, and I read somewhere about a Serial network.. but can't recall where.
