SFC will work.
Here's why. To some person's horror, another copy of the needed files are kept elsewhere on the hard disk. It is true that one can forcefully break this in their quest to run XP on very small drives. Windows 2000 as an example has this technology for many years. XP uses the same method.
If SP2 changes XP, and you run SFC and put in the original installation disk, wont some of the changes made by SP2 by undone? No need to get overly technical, it will go over my head, simply interested in an idiot's type answer, "SFC will still work" or "You're right, SFC wont work".