A particle question

How would I be able to stop a particle emitter emitting once the player collides with its parent( and if possible play a sound and show some GUI Text?

To stop the emitter you need to change the ParticleEmitter.emit property. To detect the collision, you'll probably need to use MonoBehaviour.OnTriggerEnter.

Read up a little on Unity's Physics, especially the part about "Triggers".

Make sure you use two colliders. One on the character (not necessary if you use a CharacterController) and one on the game object that holds the emitter script. The latter one should be marked as "isTrigger". Also - at least one of them needs to have a RigidBody component on it as well, preferably the one on the player, and it should be marked as "isKinematic".

If you don't understand what I've just wrote - try and read more of the manual, reference manual and scripting reference, and come back with more specific questions, since I don't think someone will just build your project for you...