function verLetra(arch)
{
  var alto=(screen.height-500)/2;
  var ancho=(screen.width-500)/2;
	MyWindow=window.open(arch,'MyWindow','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,width=500,height=500,left='+ancho+',top='+alto); return false;
}