A while back, I had a major 'rebuild' on my pc done by a local dealer (now gone bust and no longer around) after some really catastrophic HDD problems that I didn't have the ability to fix.
I gave him my XP Home disc so that it could be loaded after and also gave him my SP2 disc so he could put in the upgrade. All worked properly and well and I got my full system up and running - eventually.
However, I recently wanted to do an sfc check and all was going well until it asked me to put in the SP2 Pro disc. I put my disc and and, hmmm, it was not recognised. Obviously, the dealer used his own SP2 disc.
This means that I can't run sfc! I don't want to even think of trying to remove the SP2 that's in there in case it asks for the disc again and then have to go all through reloading my copy (an MS original) coz goodness knows what havoc might be wreaked!