Despite whatever feelings you may have on the "fairness" of using a keyboard and mouse controller when others are using the joysticks, here's a video on how the XCM XFPS adapter actually works. You can assign different keys on your keyboard and mouse to map to the buttons on the 360's controller (video of that after the jump).
The whole process seems pretty straightforward, and the results actually look pretty good. Call of Duty is responsive, and aiming seems much easier than using the joysticks. You'll have to use a wired gamepad, however, so Xbox 360 premium users are out another couple of bucks.
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