// a transformer en classe
function SmoothToolTips(){
window.addEvent('domready',function() {  
        return new Tips($$('.tips'), {
        initialize:function(){
            this.fx = new Fx.Style(this.toolTip, 'opacity', {duration: 400, wait: false}).set(0);
        },
        onShow: function(toolTip) {
            this.fx.start(1);
        },
        onHide: function(toolTip) {
            this.fx.start(0);
        }
});
    });
}