[CS3] Setting variables through button press for scripted animation

Need some help in getting the following working:

import mx.transitions.Tween;
import mx.transitions.easing.*;

onEnterFrame = function () {
    var SQUARE_y:Tween = new Tween(square, "_y", Strong.easeOut, START_y, END_y, 1.5, true);
go_0.onRelease = function() {
    START_y = square._y;
    END_y = go_0._y+50;

What’s supposed to happen is when you click button “go_0”, the object “square” will animate moving down.

Thanks in advance.