Windows, Linux, and Mac OSX support HID (Human Input Device) standards for USB keyboards, pointing devices, game controllers, and other input devices. The XBOX uses USB standards for controller ports and memory card slots. There is already a USB adapter available from Lik-Sang:
http://www.lik-sang.com/info.php?category=83&products_id=2154&

Normally, HID support would be implemented into an operating system. In the future, it would be nice if an OpenXDK developer could compile an application that includes HID support. A console emulator with support for USB game controllers would be great.