Rather than hiding elements / menu sections via the modules
system.xml (even though this might be necessary in some cases) I'd suggest you to create new a new user and user group and assign permissions based on the requirement for this user.
This should be a preferred way if the user that is to be restricted is nowhere close admin-permissions and/or the menu that is to be disabled for one user is required by other users.
You can create new user groups (aka "roles") from
System > Permissions > Roles You can then switch the
Resource Access to
Custom in the second tab and grant privileges to needed areas only:
The new role than can be applied to a particular user under
System > Permissions > Users in the tab