La verdad es que lo probe y va genial
Código HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Agregar</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<script language="javascript" type="text/javascript" src="js/mootools.js"></script>
<script language="javascript" type="text/javascript" src="js/mooValidation.js"></script>
</head>
<body>
<form class="formulario" id="form" method="post" action="index.php/abm/agregar/">
<fieldset>
<div class="fm">
<label for="titulo">Titulo:</label>
<input name="titulo" class="required" type="text" value="" />
</div>
<div class="fm">
<label for="nota">Nota:</label>
<textarea id="nota" name="nota" class="required"></textarea>
</div>
</fieldset>
<input class="submit" name="Submit" value="Guardar" type="submit" />
</form>
<script type="text/javascript">
var valid = new Validation('form');
</script>
</body>
</html> En este caso, los dos campos del form son requeridos, class="required". No te olvides de incluir los ficheros:
<script language="javascript" type="text/javascript" src="js/mootools.js"></script>
<script language="javascript" type="text/javascript" src="js/mooValidation.js"></script>
Saludos.