function changeOnglet(onglet, contenu_id) {
  var last_contenu = null;
  
  $$('.contenu').each(function (c) {
    if(c.readAttribute('selected')==1) {
      last_contenu = c;
    }
  });

  var last_onglet = null;
  onglet = Element.extend(onglet);
  var trieur = Element.extend(onglet.parentNode);
  var onglets = trieur.childElements();

  onglets.each(function (o) {
    if(o.hasClassName('selected')) {
      last_onglet = o;
    }
  });

  if(last_contenu != null) {  
    last_contenu.setAttribute('selected',0);
    Effect.Fade(last_contenu, { duration: 0.5, queue: 'front' });
    if(last_onglet != null) {
      last_onglet.removeClassName('selected');
    }
  }
  onglet.addClassName('selected');
  $(contenu_id).setAttribute('selected',1);
  Effect.Appear(contenu_id, { duration: 0.5, queue: 'end' });

  return false;
}