Ok in the forum functions.inc do a search for the function plugin_dopluginsearch_forum and replace the first part with:
Text Formatted Code
function plugin_dopluginsearch_forum($query, $datestart, $dateend, $topic, $type, $author, $keyType, $page, $perpage)
{
global $LANG_GF01, $_TABLES, $_GROUPS;
// Make sure the query is SQL safe
$query = trim(addslashes($query));
$sql = "SELECT ft.id, ft.date, ft.subject AS title, ft.comment AS description, ft.views AS hits, ft.uid, "
. "CONCAT('/forum/viewtopic.php?showtopic=', ft.id) AS url "
. "FROM {$_TABLES['forum_topic']} ft, {$_TABLES['forum_forums']} ff "
. "WHERE ft.forum = ff.forum_id AND (ff.grp_id IN ('" . implode( "','", $_GROUPS ) . "')) AND ft.date <> 1 ";