я так пробую.
$id = $article_id['id'];
$tag_arr = explode(', ', articles::tagline('id'));
// Получаем id таких же тегов
foreach ($tag_arr as $tag){
$req =mysql_query("SELECT id FROM cms_articles_tags WHERE tags = '$tag' AND article_id<>'$id' LIMIT 5");
if (mysql_num_rows($req)) {
while ($tagitem = mysql_fetch_assoc($req)) {
$id_target[] = $tagitem['id'];
}
}
}