windows xp sp2 is still unofficially released, so what you got may be a beta, or some release candidates.

when beta testing softwares (especially service packs), try to do it on a different computer first before applying it to your "main" computer. but that's for the "next time".

at the moment, you may try to use the recovery function in the windows xp installer to bring your system back to the old system files. warning: results are unpredictable.