Some people are linking to an article from GameInside in Korea showing what they believe to be a mouse for the Xbox 360.
No, it's not a mouse. What mouse would have the button in the middle of the damn palm rest?
From the looks of it, it would the Xbox 360 Wireless Controller Adaptor for Windows. It has a similar form-factor and light placement to my Microsoft wireless keyboard adaptor, and the button in the middle is most likely used to "connect" the wireless controller to the PC.