How to require login for navigation menu items?

On my navigation bar, guests can see "chat", but when they click on it, it requires them to login first to view the chats. So how can I do the same for Forums, Music, Members, pretty much anything else? Is there something in the chat.php file that causes this? I want guests to still see these options on the navigation bar, but not be able to click and view them until after they login. Thanks

chat has this:

$logged['member'] = member_auth( 0 );

add after:

check_logged();

in most case

thanks alot, that helps, but I cant find check_logged in the forum file. To do this to the forum, I assume I should be editing the index.php file found in the Orca folder, right?