function center(objdiv){
var agt = navigator.userAgent.toLowerCase();
var isMac = (agt.indexOf('mac') != -1);
var isOpera = (agt.indexOf("opera") != -1);
var isIE = ((agt.indexOf('msie')!=-1 && !isOpera && (agt.indexOf('webtv')==-1)) && !isMac);
var largeur_fenetre = (isIE?document.body.clientWidth:window.innerWidth);
//alert(largeur_fenetre);
var pos_left = largeur_fenetre/2 - 325;
//alert(pos_left);
document.getElementById("calque_menu").style.left = pos_left;
document.getElementById("calque_contenu").style.left = pos_left;
}