nicht angemeldet
$result = mysql_query("SELECT * FROM forum WHERE thema LIKE '%$suche%' OR nachricht LIKE '%$suche%' LIMIT 20",$db);
das müsste mMn $result = mysql_db_query(" .... "); heißen.
"Note: This function has been deprecated since PHP 4.0.6. Do not use
this function. Use mysql_select_db() and mysql_query() instead."
http://www.php.net/manual/en/function.mysql-db-query.php