var ns6 = (!document.all && document.getElementById);
var ie4 = (document.all);
var ns4 = (document.layers);

function showLayer(layerName) {

  var layerImageName = layerName + "Image"
  if (ns6) {
    if ( document.getElementById(layerName).style.display == '' ) {
		document.getElementById(layerName).style.display = 'none';
	} else {
		document.getElementById(layerName).style.display = '';
	}
  } else if (ie4) {
    if ( document.all[layerName].style.display == '' ) {
		document.all[layerName].style.display = 'none';
	} else {
		document.all[layerName].style.display = '';
	}
  } else if ( ns4) {
    if ( document.layers[layerName].display == '' ) {
		document.layers[layerName].display == 'none';
	} else {
		document.layers[layerName].display == '';
	}
  }
}