I truely like the way vBulletin.nl's forum is structured.
How can you detangle the forums into separate boxes and have the child-forums within these boxes, like on this forum: Announcements, General vBulletin Fan Chat, In 't Nederlands!, etc.

How is this done?

Any help is appreciated.

If you add a forum and set the option' act as forum ', to NO, it will behave as a category.
Categories are split with the professional style which you purchased.