function derecha(e) {
if (navigator.appName == 'Netscape' && (e.which == 3 || e.which == 2)){
return false;
}
else if (navigator.appName == 'Microsoft Internet Explorer' && (event.button == 2)){
}
}
document.onmousedown=derecha
   function event_false() {
         window.event.returnValue = false
   }
document.onselectstart = event_false