I have never had an emulator before. I downloaded Nestopia and it works fine using my keyboard. I went to GameStop and the guy suggested I buy an Xbox 360 controller. I plugged it into my computer and downloaded the appropriate software from microsoft.com. However, my computer recognizes it but Nestopia doesn't. When I go to Input, the area that says "Joystick" is faded out. What should I do?

I have Windows XP and a (non-wireless) Xbox 360 controller.