[jQuery] Auto Tabbing using Jquery, Please help

Hi
I am trying to do the auto tabbing text field --> text field and
Text field--> check box. My code is not working. Any one please help.
Here is my code.
<html>
<head>
<title>Check Box</title>
<script src="jquery.autotab.js" type="text/javascript"></script>
<script type="text/javascript">
(document).ready(function() {
    $('#area_code').autotab({ target: 'number1', format: 'numeric' });
    $('#number1').autotab({ target: 'number2', format: 'numeric',
previous: 'area_code' });
    $('#number2').autotab({ previous: 'number1', format: 'numeric' });
    $('#number2').autotab({ target: 'sex', format: 'All' });
});
</script>
</head>
<body>
<b>Auto Tabbing</b>
<form>
<div><strong>Phone Number:</strong><div>
<input type="text" name="area_code" id="area_code" maxlength="3"
size="3" /> -
<input type="text" name="number1" id="number1" maxlength="3" size="3" /