How to Use this Function

programming flash
1

onClipEvent (load) {
targetX = 2;
targetY =60;
vx = 0;
// our current velocity
// play with these next to values to get desired amount of springyness
springSpeed = .2;
// higher values make spring move faster
springDamp = .8;
// lower values make more resistance (friction)
this.onEnterFrame = function(roll) {
var diffX = targetX-this._x;
var diffY = targetY-this._y;
vx += diffXspringSpeed;
vx += diffYspringSpeed;
vx *= springDamp;
this._x += vx;
this._y += vx;
if (Math.abs(diffX)<1 && Math.abs(diffY)<1 && Math.abs(vx)<.1) {
this._x = targetX;
this._y = targetY;
vx = 0;
//delete this.onEnterFrame;

            }
    };

}

Its a spring type effect, it works on enterframe, but hwo can i get ti to work on my rollover?