There has been quite a buzz from the Sega’s USB Saturn controllers. Even though they are very cool products, there are a number of people that would like to take their exisiting Saturn controllers and hack into their own USB controller.
There is an excellent guide at GameSX.com that walks you through the entire process and has plenty of pictures to illustrate your journey.
I also recommend that you check out GameSX.com’s main page for a ton of other modding ideas and instructions. It will give you numerous examples of ways to turn your classic consoles and accessories into the perfectly customized device for you.