Permissions on menu adminisration

Hallo

I'm making a Drupal site whith several levels of admins: I am the top admin allowed to make all changes. Besides that I have 15 people (role "subadmin") who maintain the site. They should have proper rights to do so.

I found out that I can not finetune the permissions system the way I want it...

For the moment I struggle with these problems:
1) "administer menu": Assigning this permission allows people to change everything related to menu's. But I do not want my 15 subadminpeople to make changes to the "Navigation menu", only to the "Primary links" menu (where the content of the website is organised). So they should be able to
a) assign nodes to menu's AND
b) be able to see only the "Primary links" in admin/build/menu.

I found http://drupalmodules.com/module/menu-subtree-permissions which partly solves the problem (a is ok, b isn't). Is there another/better way to solve this problem?

2) A smaller problem. I assigned the permission "administer users" to my 15 subadmins. I also use the Gallery module. This module adds one right to the "administer users permission: a menu "Gallery Users" show up in the Navigation menu of the subadmins. Actually they shouldn't see this one. Is there a way to hide it for them? I should still be able to see it...

Thanks a lot for any help.