var menuActive = 0;
var oldLayer;

function showLayer(layerName) {
 if(menuActive == '1') {
 clearMenu(oldLayer);
 }

 if (document.all) {
    document.all[layerName].style.visibility = "visible";
  }
  else if(document.layers) {
    document.layers[layerName].visibility = "show";
  }
  else if(document.getElementById) {
    document.getElementById(layerName).style.visibility = "visible";
 }
 menuActive = 1;
 oldLayer = layerName;
}

function hide(layerName) {
  if (document.all) {
    document.all[layerName].style.visibility = "hidden";
  }
  else if(document.layers) {
    document.layers[layerName].visibility = "hidden";
  }
  else if(document.getElementById) {
    document.getElementById(layerName).style.visibility = "hidden";
 }
}

function btnTimer(layerName) {
  setTimeout("hide('"+layerName+"')", 1800);
 }

function clearMenu(layerName) {
  hide(layerName);
 }