window.addEvent('domready', function(){
 var scroll = new Fx.Scroll('demo-wrapper', {
   wait: false,
   duration: 1500,
   transition: Fx.Transitions.Quad.easeInOut
 });

 $('nav_home').addEvent('click', function(event) {
  event = new Event(event).stop();
  scroll.toElement('content_home');
 });

 $('nav_portfolio').addEvent('click', function(event) {
  event = new Event(event).stop();
  scroll.toElement('content_portfolio');
 });

 $('nav_about').addEvent('click', function(event) {
  event = new Event(event).stop();
  scroll.toElement('content_about');
 });

 $('nav_blog').addEvent('click', function(event) {
  event = new Event(event).stop();
  scroll.toElement('content_blog');
 }); 
  $('nav_contact').addEvent('click', function(event) {
  event = new Event(event).stop();
  scroll.toElement('content_contact');
 }); 
});