var strLastLayer;

function changeLayers(strCurrentLayer) {
  if (strLastLayer) hideLayer(strLastLayer);
  showLayer(strCurrentLayer);
  strLastLayer = strCurrentLayer;
}

function showLayer(strCurrentLayer) {
  var strLayerToShow = getElemRefs(strCurrentLayer);
  if (strLayerToShow && strLayerToShow.css) strLayerToShow.css.visibility = "visible";
}

function hideLayer(strCurrentLayer) {
  var strLayerToHide = getElemRefs(strCurrentLayer);
  if (strLayerToHide && strLayerToHide.css) strLayerToHide.css.visibility = "hidden";
}

function getElemRefs(strCurrentLayer) {
	var objElement = (document.getElementById) ? document.getElementById(strCurrentLayer) : (document.all) ? document.all[strCurrentLayer] : null;
	if (objElement) objElement.css = (objElement.style) ? objElement.style : objElement;
	return objElement;
}