var ie = (document.all)?1:0; // IE4
var ns4 = (document.layers)?1:0; // Netscape 4
var ie5 =(document.getElementById)?1:0; // DOM3 = IE5+, NS6

function ficha() {

if (ns4) {

  if (document.myLayer.visibility == 'show')
  document.myLayer.visibility = 'hide';
  else 
  document.myLayer.visibility = 'show';
  }

else if (ie) {

if (document.all.myLayer.style.visibility == 'visible')
    document.all.myLayer.style.visibility = 'hidden';
    else 
    document.all.myLayer.style.visibility = 'visible';
    }

else if (ie5) {

  if (document.getElementById('myLayer').style.visibility = 'visible') 
  document.getElementById('myLayer').style.visibility = 'hidden'; 
  else  
  document.getElementById('myLayer').style.visibility = 'visible'; 
  }
}