function muestra(parte) {
   if (document.getElementById){
     document.getElementById(parte).style.visibility = "visible";
   } else if (document.all) {
      eval(parte+'.style.visibility = "visible"');
   } else if (document.layers) {
      eval('document.'+parte+'.visibility = "visible"');
   }
 }
function oculta(parte) {
   if (document.getElementById){
     document.getElementById(parte).style.visibility = "hidden";
   } else if (document.all) {
      eval(parte+'.style.visibility = "hidden"');
   } else if (document.layers) {
      eval('document.'+parte+'.visibility = "hidden"');
   }
 }