Effect.MoveTo (See related posts)

Effect.MoveTo = Class.create();
Object.extend(Object.extend(Effect.MoveTo.prototype, Effect.MoveBy.prototype), {
  update: function(position) {
    var topd  = (this.toTop - this.originalTop) * position + this.originalTop;
    var leftd = (this.toLeft - this.originalLeft) * position + this.originalLeft;
    this.setPosition(topd, leftd);
  }
});