@Leon: the user authentication system in WB is good, but not perfect. To understand how it works, and how the menus are drawn, I would suggest you try the following:
1) using a DB Admin tool - such as phpMyAdmin - have a look at the 'pages' table in the WB database. Examine the fields there that are used to store information about which users are able to view and administer the page, and how that information is stored.
2) examine the function 'show_page()', in the class file 'class.wb.php', which lives inside the folder 'framework'. This is the function that is called to determine whether a page should be SHOWN to the current user. Note: sometimes a page is not shown, but DOES appear in the menu! - such as for pages with visibility set to 'Registered'.
3) slowly and carefully examine the 'show_menu()' function, in the file 'frontend.functions. php', in the 'framework' folder - this is the function that creates the menus. It calls functions from 'class.frontend.php', which in turn calls functions from 'class.wb.php', so it gets quite confusing to work out what's going on!
I hope this helps!