[jQuery] Validation plugin can't work with IE7?

[jQuery] Validation plugin can't work with IE7?


The following script work with FF 2.0.0.3, but not IE7, all scripts
are latest version from correspoinging web sites
=================
<html>
<head>
    <script src="jquery-latest.pack.js"></script>
    <script src="jquery.validate.pack.js"></script>
</head>
<body>
<script type="text/javascript">
    $.validator.setDefaults({
        debug: true
    });
        $().ready(function() {
                // validate signup form on keyup and submit
        $("#form1").validate({
            event: "keyup",
            rules: {
                textfield: "required"
            },
            messages: {
                textfield: "Please enter your firstname"
            }
        });
    });
</script>
<form id="form1" name="form1" method="post" action="">
<input type="text" id="textfield" name="textfield" />
<input type="submit" name="Submit" value="Submit" />
</form>
</body>
</html>
=================
error in IE show: $.validatior is null or not an object
while the same page work great with FF2.0
any comments and helps? thanks a lot!
howa