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Do the modules you want to limit access on have in their admin, whether or not anonymous or register users can post? You can say no there and let them have module access in groups admin. Just like with the newbb and news modules.
If not, then make sure you don't have any links for people to click to post on the module's pages and then just allow module admin in groups admin for all users or just registered users.
Edited because I said module admin and I meant module access, sorry!