function toggleLayer(whichLayer) {
  if (document.getElementById) {
    // standards based
    var style2 = document.getElementById(whichLayer).style;
  } else if (document.all) {
    // old ie
    var style2 = document.all[whichLayer].style;
  } else if (document.layers) {
    // nn4
    var style2 = document.layers[whichLayer].style;
  }
  if (style2.display == "none"){
    style2.display = "block";
  } else {
    style2.display = "none";
  }
}