If you will insert your 2000 cd, it will give you an option to create an emergency repair disk, which is a floppy with the essential start files on it. Or if you ever have problems just insert the cd, boot from the cd, it will start the install 2000 process. Don't worry, it just loads initial files. Just continue to the screen where it asks if you want to repair an installed version & click yes....same as the repair disk & it doesn't remove any files or programs already installed.
You can also use the command prompt:
sfc:/scannow to scan for missing or corrupt files. If you need help just open command prompt & type in sfc/help.