function afficher_cacher(id) {
	if (document.getElementById(id).style.visibility == "hidden") {
		document.getElementById(id).style.visibility = "visible";
	} else {
		document.getElementById(id).style.visibility = "hidden";
	}
	return true;
}
function afficher_cacher_menu(id,imageNumber) {
	if (document.getElementById(id).style.backgroundImage == "") {
		document.getElementById(id).style.backgroundImage = "url(img/menu/img_on_"+imageNumber + ".gif)";
	} else {
		document.getElementById(id).style.backgroundImage = "";
	}
	return true;
}