|Yes the true "repair" routine does set the OS back in terms of SP, and also browser, and of course many updates too. So you have a download or three to attend.|
Would be most wise save (copy) all your files (stuff you don't want to lose) to DVD at least, and if possible an external HD. Verfiy copies are OK, and ideally keep themup to date?
Ought to be no problemsin restoring SP3 etc. download the SP (save itto HD) and install from th HD.
Set a restore point first, even though it will likely make its own too prior to installation.