character model sinks through floor?

I have been following a tutorial using the unity 3d engine and came to the part where you use the script to make your model controllable? I'm new to unity so i'm not exactly sure how to explain it. When i run the script my sphere (which is my temporary player) just falls through the floor, as if It has no colliders.

here's the script, maybe I'm missing something?

var speed = 3.0;
var rotateSpeed = 3.0;
function Update ()
{
var controller : CharacterController = GetComponent(CharacterController);
transform.Rotate(0, Input.GetAxis ("Horizontal") * rotateSpeed, 0);
var forward = transform.TransformDirection(Vector3.forward);
var curSpeed = speed * Input.GetAxis ("Vertical");
controller.SimpleMove(forward * curSpeed);
}
@script RequireComponent(CharacterController)

How do you add a collider to the Ground?

I’ve seen this when I add a character (like the soldier from the Locomotion demo) who is 100 times too big. So you set scale to .01 to make it look right. But now the character controller is 100 times too small. So set its height to like 200 and radius to 50

Do you have a collider on your floor? Make sure to set it with one and then make sure the character is set above it a bit to start.

It's funny sometimes (for this developer); when needing to fire projectiles it seems that I can't envelop my model in a capsule collider (the projectiles collide with it), thus, I had to use a 'MeshCollider'. I then added a 'box collider' ONLY enveloping the feet (as best I could). The Character then, does not fall through the floor.

Hope this helps...