i just got my 360 back from microsoft and instead of it having the a hitachi drive in it, it came back with a benq drive

so i went on to ebay and bought a hitachi 59DJ and have the intension of swapping it over
how do i go about getting the key from the benq drive
and is there anything else that i need to do
can someone point me in the way of a tutorial if there is one???
cheers to all