Hi pdirect.
The permissions that you find under customize -> users -> Edit... -> Step 5 of 7: Access to Tables restrict access to modifying these tables and related fields under customize -> tables / fields. If on Step 4 of 7 the Tables / Fields checkbox is not selected, the user won't be able to modify those tables anyway. This does not prevent a user from adding, editing, or deleting existing items in a list such as activities, therefore the "read/write" option does not really apply. Out of the box, Method does not have a simple "read only" checkbox that applies to screens and related tables.
What you can do though, is use the Enable/Disable Field/Object (disabled) action OnScreenLoad by going to Customize -> Screens -> Edit... -> Advanced... -> Step 2 of 5 - Actions, and apply this action to every field or object in a screen that you do not wish a user to be able to edit, or delete. You would also have to apply the same action to the Delete, Save, Save & New, Clear / New buttons so that users won't be able to delete or create new records. This will essentially replicate the functionality of making that screen's tables and related objects "read only".
Hope this helps,
Denis