he can update his MarioCarts to run a fairly recent PC driving sim like Simbin's Race07. It will perform fine with his machine. you could bolt on a logitech wheel and he can drive to his heart's content. Then go to nogripracing and pick up any of their hundreds of race tracks from around the world.
Then again, the Logitech wheel is the price of a Nintendo Wii with a fit board. He could have tons of fun with that.