Particle emiter enable when material detected

I’m making a car, and I want that dust would go out from wheels. Can someone tell me where to start?

public var ParticleEmitter : GameObject;

function OnCollisionEnter( Collision : Collision )

{

ParticleEmitter.particleEmitter.emit = true;

}

function OnCollisionExit ()

{

ParticleEmitter.particleEmitter.emit = false;

}

This video right here will help you figure out what is needed to complete the following effect: - YouTube