ajax - session nereaguje

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.0/jquery.min.js"></script>
<script type="text/javascript" >
$(function() {
$(".subChat").click(function() {

var textChat = $("#textChat").val();
$("#textChat").val('');
var dataString = 'text='+ textChat+'sessid='+<?php echo $_SESSION['uss_id']; ?>;

$.ajax({
type: "POST",
url: "plugins/php/chat_form.php",
data: dataString
});

return false;
});
});
</script>

<form method="post">
<?php echo $us_chat->fetchSingle('nick');?>: <input id="textChat" name="text" type="text" value="" size="150" autofocus/>
<input type="submit" name="submitname" value="Odeslat" class="subChat"/>
</form>

if(isset($_POST['text']))
{
  $text_chat_form = $_POST['text'];
  
  $arr_trash = array(
        'text'  => $text_chat_form,
    'id_user' => $_POST['sessid'],
    );
  
    DB::query("insert into [:pref:chat]", $arr_trash);
  
}