How would I use the LookAt function? For example, I have a character that I control by clicking on a specific point on the ground. I have selection and walking working (sort of), but I have two problems. First up: I'm using the LookAt function to look at a point at the ground and then walk over there. However, the LookAt doesn't work in reverse. If I click behind the unit, it won't turn around. Second, I would like to stop it from rotating up and down, so the head is always horizontal to the ground. Here's my script currently. The variables referenced are in another script that gets the mouse input.

var MouseClick : MouseClick;
var speed = 2;

function unitSelection () {
    MouseClick.selected = true; 
    Debug.Log ("I'm selected. What can I do for you?");
}

function Update() {
    if (MouseClick.move) {      
        transform.LookAt(MouseClick.TargetDestination);         
        transform.Translate(Vector3.forward * Time.deltaTime * speed);
    }
}

How can I make this happen?

EDIT: Here lies the MouseClick script:

var selected = false;
var move = false;
var TargetDestination;

function Update () {
    if (Input.GetButtonDown ("Fire1")) {
        var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
        var hit : RaycastHit;
        if (Physics.Raycast (ray, hit)) {
            if (hit.collider.tag == "Unit") {
                    hit.collider.SendMessageUpwards ("unitSelection");

            }
            else if (hit.collider.tag == "Terrain") {
                Debug.Log ("You Missed!");
            }
        }
    }

    if (selected && Input.GetButtonDown ("Fire1")) {        
        var ray1 = Camera.main.ScreenPointToRay (Input.mousePosition);
        var hit1 : RaycastHit;
        if (Physics.Raycast (ray1, hit1)) {
            if (hit1.collider.tag == "Unit") {
                    Debug.Log ("I'm already selected!");
            }
            else if (hit1.collider.tag == "Terrain") {
                selected = false;
                Debug.Log ("You unselected!");
            }
        }
    }

    if (Input.GetButtonDown ("Fire2") && selected) {
        var ray2 = Camera.main.ScreenPointToRay (Input.mousePosition);
        var hit2 : RaycastHit;

        if (Physics.Raycast (ray2, hit2)) {
            if (hit2.collider.tag == "Unit") {
                    Debug.Log ("I'm already selected!");
            }
            else if (hit2.collider.tag == "Terrain") {
                Debug.Log ("I'm going already!");
                move = true;
                TargetDestination = Input.mousePosition;                
            }
        }
    }
}

Thanks in advance - Elliot Bonneville.