function switchlayer(Layer_Name)
{
  var GECKO = document.getElementById? 1:0 ;
  var NS = document.layers? 1:0 ;
  var IE = document.all? 1:0 ;

  if (GECKO)
       {
 document.getElementById('u1').style.visibility='hidden';
 document.getElementById('u2').style.visibility='hidden';
 document.getElementById('u3').style.visibility='hidden';
 document.getElementById(Layer_Name).style.visibility='visible';
 }
   else if (NS)
       {
 document.layers['u1'].visibility='hidden';      
 document.layers['u2'].visibility='hidden';      
 document.layers['u3'].visibility='hidden'; 
 document.layers[Layer_Name].visibility='visible';   
 }
  else if (IE){
 document.all['u1'].style.visibility='hidden';
 document.all['u2'].style.visibility='hidden';
 document.all['u3'].style.visibility='hidden';
 document.all[Layer_Name].style.visibility='visible';
 }
}

function closelayer() {
  var GECKO = document.getElementById? 1:0 ;
  var NS = document.layers? 1:0 ;
  var IE = document.all? 1:0 ;

  if (GECKO)
       {
 document.getElementById('u1').style.visibility='hidden';
 document.getElementById('u2').style.visibility='hidden';
 document.getElementById('u3').style.visibility='hidden';
 }
  else if (NS)
       {
 document.layers['u1'].visibility='hidden';      
 document.layers['u2'].visibility='hidden';      
 document.layers['u3'].visibility='hidden';    
 }
  else if (IE){
 document.all['u1'].style.visibility='hidden';
 document.all['u2'].style.visibility='hidden';
 document.all['u3'].style.visibility='hidden';
 }
}