// ////////////////
// hide a layer
function hideLayers (layerName) {
         if (layerExists(layerName)) {
             if (client.isNS6){
                document.getElementById(layerName).style.visibility = "hidden";
             } else {
                eval (doc + layerName + sty + ".visibility = 'hidden';")
             }
         }
}
// ///////////////////////
// show a layer
function showLayers (layerName) {
     if (layerExists(layerName)) {
        if (client.isNS6){
                document.getElementById(layerName).style.visibility = "visible";
        } else {
                eval (doc + layerName + sty + ".visibility = 'visible';")
        }
     }
}

function layerExists(layerName) {
         if (client.isIE){
              return document.all[layerName];
         } else if  (client.isNS4)  {
                return document[layerName];
         } else {
               return document.getElementById(layerName);
         }
}