muhibmc, who described correctly the whole process for upgrading to backlit, wrote at a certain point: "**there will also be a clear film right under the black one, you do not have to remove that one." well, after performing the same operation with success, I can tall you DO have to replace the original clear sheet instead, wich you find behind the keyboard, with the new "white-dotted" one coming with the backlit spare part. I think you *may* even leave it and install the backlit components behind it as well, but I don't think the original backlit Macbooks feature two clear plastic films one behind the other. I guess they have the backlit only.
Please search further through previous solutions, this matter was already discussed widely. Anyway, I did already what you are planning to do and the result is excellent. Just buy one of those 20$ backlit panels on eBay and go! Keyboards are exactly the same (except F5 and F6 keys not showing the symbols for tuning backlight intensity, but I guess you can survive this...) (ps: ensure your Macbook's mainboard features the backlit connector before proceeding...some people say some of the first unibody Macbooks are missing this connector). Hope this helped.