Как вариант...
<!DOCTYPE html>
<html>
<head>
<script src='http://code.jquery.com/jquery-latest.js'></script>
<!--
<link rel='stylesheet type=text/css href=tmp.css' />
-->
<style type='text/css'>
</style>
<script type='text/javascript'>
$(function (){
$('form .sort').change(function (){
var id=$(this).parent().prev().find('.cat_id').val();
alert(id);
});
});
</script>
</head>
<body>
<form action="#" method="get">
<table>
<tr>
<td><a href="#">cat_name</a></td>
<td><input class="cat_id" value="id"/></td>
<td><input class="sort" name="sort" type="text" name="order_cat" size="1" value=""/></td>
</tr>
</table>
</form>
</body>
</html>