I managed to fixed my friend's XP system by figuring out which service was missing and then finding its dependencies. Turns out it was missing a driver file. I copied the driver file from one of my old systems and used it in his.
I would just think that there has to be another option to those who lose their OS CDs. Because TBH the only reason my old desktop still runs is because I've taken good care of it but once the HDD dies then that box is getting Linux because I don't remember where I put OS CDs for that thing. But I guess I have to take better care of things too