<!-- DEBUT MENU DEROULANT HORIZONTAL -->
   function ouvrir(sousmenu){
        document.getElementById(sousmenu).style.visibility="visible";
   }
   function kill(sauf){
	document.getElementById('compania').style.visibility = "hidden";
	document.getElementById('sierra').style.visibility = "hidden";
	document.getElementById('canyon').style.visibility = "hidden";
	document.getElementById('pluri').style.visibility = "hidden";
	document.getElementById('rando').style.visibility = "hidden";
	if (sauf!="tous"){
	   document.getElementById(sauf).style.visibility = "visible";
        }
   }
<!-- FIN MENU DEROULANT HORIZONTAL -->