Check out this tut. It's an exploding wall. You could do your cardboard animation in a similar fashion. The nail could act sort of like the projectile and the cardboard could act like the wall. I havn't really done any animation, this was just what came to mind when I read your thread.
If you use this method, then I think you'll need to perform the boolean (as Jr. Who suggested) to make the nail hole before you create the shatter (crack) effect.
Edit: instead of using a force to blow your cardboard away, just set keys to move the cracked pieces as you want. Also, maybe you can use a deform tool and set keys for it to create the bending effect.
Don't be satisfied with what you can do but rather strive to do the things you can't do!