BoGdAn, так правильней будет
$lu = mysql_fetch_array(mysql_query("SELECT `id`, `name`, `datereg` FROM `users` ORDER BY `datereg` DESC LIMIT 1") ); BoGdAn, так правильней будет
$lu = mysql_fetch_array(mysql_query("SELECT `id`, `name`, `datereg` FROM `users` ORDER BY `datereg` DESC LIMIT 1") );