An ITB is something that fits onto the engine in place of the manifold, and allows air directly into each cylinder. they sound really nice, and they are a good way to gain extra HP, but they can be very expensive. I wouldn't recommend putting one on a BMW, BMW engineers are very intelligent people, and they design stuff right the first time. If he was to modify his BMW this way, he would have to find a shop that could retune his ECU to work with the new intake setup. This would be necessary, or it could really hurt his car. Check your area for tuning shops, and have him call them and ask for thier advice, they are, after all, proffesionals. I would also tell him to meet with any people he wants to work on his car, a lot of these "tuners" are used to working on imported cars (honda, acura, mitsubishi...), and many people aren't familiar with BMWs, so make sure they know wtf they're doing before handing them your car!