How can I enable moderator role's ability to administer users only apply to certain user roles? I am making a Drupal (v7.8) website with several user roles, including Super User, Admin, Moderator, Editor, and Reviewer. I want the Moderator role to be able to use the privileges that Administrate Users gives, but only for roles "below" Moderator (i.e. Editor and Reviewer).

I haven't been able to find a module or documentation on how to do this.

Thanks!
There is quite a new contrib module called "Permissions subset" for D7 you could test if it meets your requirements.