Help Arduino, Leds and sensors

Hi, I’m new in the forums and in the Arduino world. On the one hand, I’m looking for the way to connect about 300 tricolored leds to an Arduino. What I want is, through my PC, to ask the Arduino to switch on the leds in a determined order and with a determined color. On the other hand, I need some switching sensors to inform the PC when they detect a movement. Does anybody know the codes that I need? Thanks everyone for any help.

On the one hand, I’m looking for the way to connect about 300 tricolored leds to an Arduino.

Connect one leg of each LED to a separate digital pin. You did get an Arduino with 900 digital pins, didn't you?

How do you intend to power 900 LEDs? Have you given any thought as to how much power is required?

LED power - if only one is on at a time that's only 3 x 20mA. What is your plan to lay them out? Some kind of matrix? Big long string?

What kind of movement detection is needed? I wired up this one yesteday. http://www.sparkfun.com/products/8630

Had to read its output via analog, open collector output doesn't seem to go low enough to trigger a digital interrupt, when powered from 3 AA batteries anyway. http://itp.nyu.edu/physcomp/sensors/Reports/PIRMotionSensor

Take a look at this http://www.amazon.com/5050-Digital-Flexible-LED-Strip/dp/B004AGVKHW digitally controlled RGB strip lighting.

Arduino library! http://code.google.com/p/ledstrip/