jquery validate 不验证的问题

<!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>
    <script src="Scripts/jquery-1.4.1.js" type="text/javascript"></script>
    <script src="Scripts/jquery.validate.js" type="text/javascript"></script>
    <script src="Scripts/jquery.metadata.js" type="text/javascript"></script>
    <title></title>
    <script type="text/javascript">
        $(document).ready(function () {
            $("#commentForm").validate({ meta: "validate" });
        })
    </script>
    <style type="text/css">
        *{font-family:Verdana;font-size:96%}
        label{width:10em;float:left;}
        label.error{float:none;color:Red;padding-left:.5em;vertical-align:top;}
        p{clear:both}
        .submit{margin-left:12em;}
        em{font-weight:bold;padding-right:1em;vertical-align:top;}
        
    </style>
</head>
<body>
<form id="commentForm" method="get" action="#">
    <fieldset>
        <legend>验证例子</legend>
        <p>
            <label for="username">用户名</label>
            <input type="text" name="username" id="username" size="25" class="{validate:{required:true,minlength:2}}"/>
        </p>
        <p>
            <label for="cemail">邮件</label>
            <input type="text" name="cemail" id="cemail" size="25" class="{validate:{required:true,email:true}}"  />
        </p>
        <p>
            <label for="curl">网址</label>
            <input type="text" name="curl" id="curl" size="25" class="{validate:{url:true}}" />
        </p>
        <p>
            <input type="submit" class="submit " value="提交" />
        </p>
    </fieldset>
</form> 
</body>
</html>
提交的时候不进行验证，直接提交了。哪位大能能帮我看看