window.addEvent('domready', function(){
       //do your tips stuff in here...
       var zoomTip = new Tips($$('.zoomTip'), {
          className: 'custom', //this is the prefix for the CSS class
          initialize:function(){
             this.fx = new Fx.Style(this.toolTip, 'opacity', {duration: 500, wait: false}).set(0);
          },
          onShow: function(toolTip) {
             this.fx.start(1);
          },
          onHide: function(toolTip) {
             this.fx.start(0);
          }
       });
    });