A computer with Arduino and Processing. Try to get the most up-to-date release
e and http://processing.org/download/
An Arduino(make sure it has PWM outputs, which is all/most)
USB cable(for the Arduino)
If you are using more than one RGB, you may need to calculate the different values for the resistors. Follow this tutorial http://www.sparkfun.com/tutorials/219
or use this site http://led.linear1.org/led.wiz
to calculate the required resistances.