I have installed Drupal 6 with more than 100 Modules and many blocks. I have just recognized that changes under admin/modules has no effect and no feedback like "Your changes ... successfully". Because Drupal never gets the _POST request as there are too many input fields that Suhosin can not handle. Just deacticated Suhosin, restarted Apache and all perfect. Not looking for a solution to do it without deactivating Suhosin.