Need help with registry

Somewhere in the registry of Windows is where all the registration codes are kept with programs you load into a computer. I am having problems trying to find these codes on my system. I contracted a virus and need to debug and reinstall my O/S’s I am running Win98 and Win2000. Some of the programs I installed I have lost some of my sleeves that had my registration codes on them. Can someone point me in the direction as to find these?