Drag movieclip on Y-axis

Hi,
Is it possible to drag a movie clip named "xxxx" along the y axis when you click and drag? if so what is the as2 code?

Actionscript Code:

xxxx.onMouseDown = function() {
    if(this.hitTest(_root._xmouse, _root._ymouse, true)) {
        this.onMouseMove = function() {
        this._y = _root._ymouse;
        updateAfterEvent();
        }
    }
}
xxxx.onMouseUp = function() {
    delete this.onMouseMove;
}

gparis