I "think" its Jack Smirking Revenge ~ The Dust Brothers. Score was written specifically for the film, they only had a budget of 60 million for the film and 8 million of the was blown on Brad Pitts fee.
Having looked at the OST for the movie on Amazon the one review said this :
"My favourite track of the bunch is "Jack's Smirking Revenge". The track begins off with a sense of realisation, and turns into a feeling of knowing what to do. In this case it would be Jack's revenge on his boss."
(even though Norton's character isn't called Jack)
well done people :)
put fight club in to download some of the tracks and it was just dust brothers tracks ....
so i didnt know which one it was- and theres about 11 of them and thy all sound the same,
:)