On my computer, I was able to map the buttons on the same screen that the keys can be mapped. IIRC, it's Controller Setup or Button Configuration. But you have to plug the controller before starting the game.
I am always wrong in this website, and I only notice it because someone always says "read further down" to me.
Are you using the wireless 360 controller? Unfortunately, they didn't make the wireless one compatible, it doesn't properly read it as an xinput device, so you can't map the triggers to anything. Only the wired controller works. It sucks, but if you have no other choice for controllers, might I suggest using xpadder? It's not quite the same, but you can bind keyboard inputs to the 360 controller.