Subforums that acts like a thread

[Ducks]

I hope I can manage to explain this so it's easy to understand.

I'm looking for a mod that allows users to create a thread, but the thread should act like a subforum, so you can post threads inside that thread with a thread overview. The main thread should appear in the "real" forum list (the standard) as a thread.

Let's say I have a section called Sport, and in that I've a category called Soccer. A regular user should then be able to start af thread about ie. UEFA 2008, but instead of messing everything up in a long thread, the thread he starts in "Soccer" should act as a subforum/folder where others can post about UEFA 2008 too.

Forum
- Sport
- - Soccer
- - - UEFA 2008
- - - - Thread1, who do you think will win
- - - - Thread2, what's your favourit team

Hope it's clear? Hard to explain