Apple Mail And Folder Management

I use Thunderbird on Windows, but from time to time like to fire up Apple Mail when on my Mac.

Why is it Apple Mail on Leopard doesn’t seem to allow me to view a few mailboxes nested under the inbox on an IMAP account? I haven’t tried under POP3, though I’d venture it’s the same limitation.

You would think they would at least show it linear if it couldn’t display it under inbox. Instead what it does is just not show it. Perhaps it’s important for me to be able to presort my inbox to make it manageable.