function cambia(op)
{
 nav=navigator.appName;
 if (nav=="Netscape")
 {document.getElementById(op).src= "img/"+op+"2.jpg";}
 else
 {
 document.all[op].src = "img/"+op+"2.jpg";
 }
 
}
function vuelve(op)
{
if (nav=="Netscape")
 {document.getElementById(op).src= "img/"+op+"1.jpg";}
 else
 {
 document.all[op].src = "img/"+op+"1.jpg";
 }
}