Notice how he uses a 12v wire in that link from the disk drive? there is also going to be a 5v wire there somewhere.
(12v) can cause it to burn out prematurely
if you want to trigger any inputs from the 360, you will need a second power point on the board.
Sorry, what do you mean there is also going to be a 5v wire there? Do you mean a different gauge of wire? Would the gauge of wire coming from the XBOX be different than the wire going into the Arduino? I know I've still got a lot to learn so excuse any stupid questions.
My (possibly incorrect) recollection from reading about the Xbox is that it has a USB interface (with non-standard connectors) for peripherals. Why not tap into the 5V and ground on that bus? You could use an extension cable or damaged gamepad to get a connection, and avoid doing any modification to the console.
Is it possible that this might not be enough power to run two servos?
However, there's also a good chance that they included enough capacity to run the motors in "force feedback" game controllers. You need to do careful research.