Controling leds with arduino.

Hello everyone,i want to make somethin for christmas and i have to use
rgb leds on this one ,the problem is that i need more than the outputs of the arduino since im going to use more than 12 rgb leds .
Is there any solution on this one ?
I was thinking of conecting a mondomatrix ledmatrix with my arduino duemilanove but i dont know if it is possible to get them talking to each other .
Any suggestion accepted.
Thanks …

The problem with RGB LEDs is that they use 3 channels of control for every LED so controlling 12 is like controlling 36 normal LEDs. You need some external form of control. Now do you want them just on and off or do you want to be able to dim them?
Next you need to decide how bright they must be. If as bright as possible then you will need a controller for each LED if not then you can multiplex them.
A popular choice is the TLC5940 controller, you can control 16 LEDs with this so for 12 RGB LEDs you will need three. You can multiplex them as shown here:-

yes i want to fade them too in order to make different colors.

I just ordered 5 of the TLC5940 chips through TI’s free sample program, but they are back ordered. They expect to this in mid November.

Yes the TL5940 chips have been a bit in short supply for the last year or so, but they are available now if you don't mind paying:-