Have you, as Admin, looked at the
permissions facility when you are in the outer most layer of your Nabble software:
Select Options > Users > Change permissions, and Manage users and groups?
Using these, you can control who has access to what, but as things stand at present, you will have to maually move registered users to a specialist group. However, Nabble are working on new templates to give us more control across all areas... and it may just be that this is one feature that might be included... hopefully!
Edit: Greg... you beat me to it!
Anne