$.post does not work? why?

$.post does not work? why?

Why this line never work?

$.post("external mail.php file", $("#commentForm").serialize());

Thanks
Here is my form,

  1. <script src='https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js' type='text/javascript'/>
    <script src='http://dev.jquery.com/view/trunk/plugins/validate/jquery.validate.js' type='text/javascript'/>
    <script type='text/javascript'>
    /*<![CDATA[*/
    $(document).ready
    (
    function()
    {
    $("#commentForm").validate
    ({

    submitHandler: function()
    {

    $.post("external mail.php file", $("#commentForm").serialize());
    $("#commentForm").slideUp
    ("normal", function()
    {
    $("#commentForm").replaceWith('<h1>Success</h1><p>Your email was sent.</p>');
    }
    );
    return false;
    }
    });
    }
    );
    /*]]>*/

    </script>






























  2. <style type="text/css">


  1. label.error { float: none; color: red; padding-left: .5em; vertical-align: top; }
    </style>
    <form class="cmxform" id="commentForm" method="post" action="">
    <fieldset>
    <legend>You can submit here</legend>
    Name
    <em>*</em><input id="cname" name="name" size="25" class="required" minlength="2" />
    E-Mail
    <em>*</em><input id="cemail" name="email" size="25" class="required email" />
    URL<input id="curl" name="url" size="25" class="url" value="" />
    Your comment
    <em>*</em><textarea id="ccomment" name="comment" cols="22" class="required"></textarea>
    <input class="submit" type="submit" value="Submit"/>
    <input type="reset" class="reset" value="Reset" />
    </p>
    </fieldset>
    </form>