Tell your nephew to play it on his PC? If it can't handle it, just upgrade it enough so it can handle low/medium settings (it'll be cheaper than you buying a PS3 for 1 bloody game). Even at low/medium settings it's going to look a hell of a lot better than PS3 and most importantly the controls won't be TERRIBLE.
For someone who's become accustomed to the accuracy and speed of a mouse, playing first person shooters with a gamepad feels like going back into the stone age.