ns4 = ( document.layers ) ? 1 : 0;
ie4 = ( document.all ) ? 1 : 0;

function show(id) {
 if (ns4 && document.layers[id] ) document.layers[id].visibility = "show"
 else if (ie4) document.all[id].style.visibility = "visible"
}

function hide(id) {
 if (ns4 && document.layers[id] ) document.layers[id].visibility = "hide"
 else if (ie4) document.all[id].style.visibility = "hidden"
}

function switchLayer( s , h )
{
  hide( h );
  show( s );
}

function showLayers()
{
   for( i = 0; i < document.layers.length; i++ )
   {
      alert( document.layers[i].name );
   }
}