var cur_lyr;	// holds id of currently visible layer
	function swapLayers(id) {
	  if (cur_lyr) hideLayer(cur_lyr);
	  showLayer(id);
	  cur_lyr = id;
	}
	
	function showLayer(id) {
	  var lyr = getElemRefs(id);
	  if (lyr && lyr.css) lyr.css.visibility = "visible";
	}
	
	function hideLayer(id) {
	  var lyr = getElemRefs(id);
	  if (lyr && lyr.css) lyr.css.visibility = "hidden";
	}
	
	function getElemRefs(id) {
		var el = (document.getElementById)? document.getElementById(id): (document.all)? document.all[id]: (document.layers)? getLyrRef(id,document): null;
		if (el) el.css = (el.style)? el.style: el;
		return el;
	}
	
	// get reference to nested layer for ns4
	// from old dhtmllib.js by Mike Hall of www.brainjar.com
	// function getLyrRef(lyr,doc) {
	//	if (document.layers) {
	//		var theLyr;
	//		for (var i=0; i<doc.layers.length; i++) {
	//		theLyr = doc.layers[i];
	//			if (theLyr.name == lyr) return theLyr;
	//			else if (theLyr.document.layers.length > 0) 
	//			if ((theLyr = getLyrRef(lyr,theLyr.document)) != null)
	//					return theLyr;
	//	  }
	//		return null;
	 // }
	//}