You already can use a mouse and keyboard for the 360 but it will cost you about 50$-80$, this is what the newer model looks like, It´s a"XCM XFPS 360 PRO" and it works with all games:
it has two wheels for adjusting mouse sensivety and you can put the gamepad buttons on any keyboard or mouse key you whant, you can put a turbo (auto fire) mode on any button, and you even get too use your old PS2 conroller, light gun, guitar or dancing mat. I´ve never played with it but I read it works very well, if I goes down in price a little I might get one as soon as I have my Falcon 360 :)
For more info and pics check here: http://www.xcm.cc/XFPS_360_PRO.htm