function creerCompte(){  
montrer();
new Ajax.Request('./serveur.php', {
 method : 'post', 
 parameters: {new:$('new').value,old:$('old').value},

 onSuccess : function(transport) {
// alert (transport.responseText) ; 
$('contenu').innerHTML=transport.responseText;
 },

onFailure    : function (errorCode) {alert("Erreur : " + errorCode)} 
 }) ;
}