Calculating Battery needs for an LED array

Hey guys, I'm trying to figure out what type of battery arrangement I'll need to drive 64 RGB LEDs. Ideally I'd like to use rechargeable batteries and have them last for roughly two hours. The other components I intend to use are SparkFun's 4x4 Button Pad Controller SPI, the 2x2 button pads, an Unsped Arduinome Shield, and an Arduino Duemilanove.

How would I go about calculating my battery needs, and do you have suggestions about the types of rechargeable batteries I should look into?

Would this by any chance me a monome?

Are the LEDs in a matrix or all on at once?

Calculate the current through one LED given the value of series resistor you are using. Then multiply that by 64 for individual LED control or by 8 for a matrix. The rest of the current draw is small by comparison. When you have the current double it and that is the mA capacity of the battery for hours for two hours of use. Add a bit (20%) to the currrent for good luck.