object to point at mouse based on mouse position

I need the object to aim at the mouse. Like a side Scrolling shooter would. right now it "Moves"....but not really where the mouse is. This is what i have for code.

var speed : float = 1.0; //how fast the object should rotate

 function Update(){
      transform.Rotate(Vector3(Input.GetAxis("Mouse Y"), Input.GetAxis("Mouse X"), 0) * Time.deltaTime * speed);
 }

that is on my gun object. I think i need to also change the rotate point on my gun any idea on how i would do that?

thanks alot Karl

I think you're looking for Transform.LookAt(). You call this on the object that you want to rotate, and you give it a Vector3 point in 3D space where you want the object to rotate to.