My code looks like so:
Actionscript Code:
onClipEvent (enterFrame) {
    xdiff = this._x-_root.cursor._x;
    ydiff = this._y-_root.cursor._y;
    hyp = Math.sqrt(Math.pow(xdiff, 2)+Math.pow(ydiff, 2));
    phi = (180/Math.PI)*Math.asin(ydiff/hyp);
    if (xdiff>0) {
        phi = 90-phi;
        this._rotation -= (0.1)*(this._rotation+phi);
    } else if (xdiff<0) {
        phi = phi-90;
        this._rotation -= (0.1)*(this._rotation+phi);
    }
}
It has some more bells and whistles to it but this is the important part.