Just a heads up that the code linked to by John has an error. The code should only target the current query, however due to the use of the global is_search() function, the filter will be applied to all queries on page load that happens to be a search.
The first snippet should be:
function cf_search_join( $join, $query ) {
global $wpdb;
if ( $query->is_search ) {
$join .=' LEFT JOIN '.$wpdb->postmeta. ' ON '. $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id ';
}
return $join;
}
add_filter('posts_join', 'cf_search_join', 10 , 2 );
Same goes forth for posts_where and posts_distinct.
