osCommerce MS2 is a bit buggy, unfortunately it will be the first version to show up in dutch Google search results.
To fix the bug where modules can not be saved, change line 46 in
admin/modules.php from
while (list($key, $value) = each($HTTP_POST_VARS['configuration'])) {
to
foreach ($_POST['configuration'] as $key => $value) {
More information about ms2 bugs can be found here (Dutch):
http://forums.oscommerce.nl/index.php?showtopic=11759