OnMouseDown carry out whole function problem

hi Im not an expert on Javascript and could really do with some help please.

Im making a flying game and want to automate some of the movements to give the feel of being flown to different locations.

I have GUI buttons set up and the following Javascript is attached to each button which in turn is parented to the camera with a target and speed set.

The problem I am having is that when you press the GUI button the camera only moves within the OnMouseDown time (less than a second) so if you set the time to say 0.5 the camera will jump to the location but I need a flowing motion. How do i set the GUI button to carry out all the motion and not as just a bit of it when it is active?

Javascript =

var normaltex : Texture2D;

var hovertex : Texture2D;

var target : Transform;

var smoothTime = 0.3;

private var velocity = Vector3.zero;

function OnMouseEnter(){

 guiTexture.texture = hovertex;

} function OnMouseExit(){

 guiTexture.texture = normaltex;

} function OnMouseDown(){

 var targetPosition : Vector3 = target.TransformPoint(Vector3(0, 5, -30));

 transform.position = Vector3.SmoothDamp(transform.position, targetPosition, velocity, smoothTime);}

Thanks in advance

J