// visualizza un layer
function displayLayer(divId) {
 if (document.all) {
   document.all[divId].style.visibility="visible"; // IE
 } else if (document.layers){
   document.layers[divId].visibility="show"; // NN4
 } else if (document.getElementById) { // Standard 
   document.getElementById(divId).style.visibility="visible";
 }
}


// nasconde un layer
function hideLayer(layerId) { 
  if (document.all) {
    document.all[layerId].style.visibility="hidden"; // IE
  } else if (document.layers){ //NN4
    document.layers[layerId].visibility="hide";
  } else if (document.getElementById) { //NN6 ed Opera
    document.getElementById(layerId).style.visibility="hidden";
  } 
}