Smooth look at on Y axis only?

Anyway to make a smooth lookat, but not change the Z and X axis, only the Y?

 

Anyone?

 

Looking for my self here, So far my lookAt scripts make the object face towards the ground upon initialiation which kinda looks funny

 

Code (csharp):

1.  
2. var target : Transform;
3. var rotSpeed : float;
4.  
5. function Update(){
6.     var targetPos = target.position;
7.     targetPos.y = transform.position.y; //set targetPos y equal to mine, so I only look at my own plane
8.     var targetDir = Quaternion.LookRotation(targetPos - transform.position);
9.     transform.rotation = Quaternion.Slerp(transform.rotation, targetDir, rotSpeed*Time.deltaTime);
10. }
11.