function toggleLayer(currentLayer, whichLayer)
{
     
     if (document.getElementById)
     {
          // this is the way the standards work
	  var style1 = document.getElementById(currentLayer).style.display = "none";
	  var style2 = document.getElementById(whichLayer).style.display = "block";
	    
     }
     else if (document.all)
     {
          // this is the way old msie versions work
	  var style1 = document.all[currentLayer].style.display = "none";
	  var style2 = document.all[whichLayer].style.display = "block";
	   
     }
     else if (document.layers)
     {
          // this is the way nn4 works
	  var style1 = document.layers[currentLayer].style.display = "none";
	  var style2 = document.layers[whichLayer].style.display = "block";
	   
     }
}