[mysql] problema con LIMIT

[StErMi]

io ho messo cosi

<?
include("config.inc.php");
$limite = 5;
$q = "SELECT * FROM user";
$num = mysql_num_rows(mysql_query($q, $db));
$q = "SELECT id, nick, nazione FROM user ORDER BY id DESC LIMIT $num, $limite";
$user = mysql_query($q, $db);
?>

ma non funziona