From: Ratedr on
Ok I hope that I am explaining this correctly:

I had an issue with windows xp, and I wanted to repair it, but for
some reason my disc (dont ask why) didnt give me a choice of
the windows I just installed another copy (now c:
\windows.1 lets say) I dont want to go through the hassle of fixing
everything, reinstalling my shortcuts, etc....I just want to be able
to repair my ORIGINAL windows installation c:\windows. Is there a
way, from the windows.1 installation, to repair the c:\windows
installation? like doing the sfc /scanow but to scan the original
windows installation?