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);

        }

    });

});