well the cd key is not stored on the disk files, ive done some research into this a while back!
some people said to go into this folder open this look for this blah blah blah didnt work cos they key isnt there...
truth is every disk is the same but all keys are different, makes sense because microsoft would have to produce 1000's of disks each one different.
you really are paying for the key!!
i have 3 windows xp disks with no key-ive aquired and there useless, unless some one tells me different....
i cant think of a way out of this for you