I need to use my arduino as a USB joypad (I really only need the buttons, no levers) so that some events from sensors could be sent to a GTK/SDL app on my PC.
Please note that I _do not_ need to connect a joypad to my arduino.
You are probably going to have your work cut out for you making an arduino appear as a game pad. Not sure really what you are looking for. I suggest you connect your sensors to the arduino, then have the arduino operate the buttons on a slightly hacked gamepad like below, which is attached to the computer. http://www.geeks.com/details.asp?invtid=PCJOYPAD-BLU-N&cat=JOY