well, the guy that made the script either left something out or doesnt have much experience with php and mysql.
he collects the proper info in the config.inc.php but none of those php scripts ever call mysql_connect.
since thats never called, mysql_query will not work.
you could edit config.inc.php after after the variable declarations put
mysql_connect($host, $db_user, $db_pass) or die(mysql_error());
mysql_select_db($db) or die(mysql_error());
since the config is incuded by all the files that need it, the db connection will be made every time.