I assume you are using a
Chicklet to interface with the XBox 360 controller.
The XBox button is not mapped to an output on the chicklet. That button is not even available on a computer, so I'm guessing you would need special, non-HID, drivers to get the buttons's state.
The port mappings for the Chicklet are available in
this manual.
EDIT: If you are looking for code not specific to the 360 controller PM or e-mail me.