Sorry if I confused you, it sounds like you gave the actual anonymous user group the permissions I described. What I meant was that you assign the permissions to the category "public", not the user group. When you assign permissions to a category you can choose which user group to associate those permissions with.
Go to tiki-admin_categories.php (the "Admin Categories" page) and click on the key icon next to the "public" category. Then you'll see what I mean. You will probably want to remove the permissions from the anonymous user group (under Admin Group), otherwise anonymous will be able to see a lot more than you originally intended.
Let me know if you need more help, it's more than possible that I'm not explaining things very clearly.