function nuevoAjax(){ 

  var req;

  if (window.XMLHttpRequest) {

    req = new XMLHttpRequest();

  } else {

    req = new ActiveXObject("Microsoft.XMLHTTP");

  }  

  return req;

}



function validar_numero(numero){

  if (!/^([0-9])*$/.test(numero)) {

	return false;

  } else {

    return true;

  }

}



function boletin(correo){

  var contenttype = 'application/x-www-form-urlencoded';

  req = nuevoAjax();

	req.open("GET", "envia_email.php?correo="+correo,true); 

  req.setRequestHeader('Content-Type', contenttype);

  req.onreadystatechange =

    function() {

      if (req.readyState == 4)

        var ok = true;

	  }

	req.send('null');

}