var max = 2000;

var Scroller = {
  pos: function() {
    return parseInt($('scroller').style.left);    
  },
  effect: null,
  right: function(x) {
    if (max > this.pos()) {
      x = x ? x : -400;
      if (!this.effect) { 
        alert('new effect'); 
        this.effect = new Fx.Styles('scroller', { onComplete:function(){ alert('finish') }} ); 
      }
      this.effect.start({ 'left': x });
    }
  }
....