The trick is to attack with enough carnage to force your opponent into over reacting and creating a divide between the west and muslims, but no so big of an attack that most muslims would feel that animosity towards muslim is justified. Imagine if OBL got a nuke and nuked NYC, the US would invade afghanistan, but I am guessing that half of the arab world would be so appalled by the nuke attack that they would fight side by side with the US against OBL. A big attack would not work, a small attack will work but not so small that the west can dismiss it.
Hitler burned down one building; the Reichstag, blamed it on the Jews and in return he got the germans to gleefully gas their former neighbours, friends, and acquaintances. Hitler did it with just a can of gasoline and a box of matches, what a knife's edge we all live on.