function validar_email(formulario,campo,campoError){
  email    = eval("document.getElementById('" + formulario + "')." + campo      + ".value");
  emailErr = eval("document.getElementById('" + formulario + "')." + campoError + ".value");
  longi    = eval("document.getElementById('" + formulario + "')." + campoError + ".value.length");
  em_val   = /^\w+@\w+(\.\w+?)/
  em_val2  = /(\.\w+?)+@\w+(\.\w+?)/
  if(em_val.test(email) || em_val2.test(email) ) {
      return true;
    } else {
      if (longi>0) {alert(emailErr)};
      return false;
  }
}