If you installed a Windows 2000 Service Pack with the uninstall option, the original version of files replaced by the service pack are stored in a hidden folder at %SystemRoot%\$NtServicePackUninstall$.
Once you determine that there will NEVER be a need to uninstall the service pack, you can perform the following procedure:
1. Delete the $NtServicePackUninstall$ sub-folder.
2. Use Regedt32 to navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Windows 2000 Service Pack n,
where n is the service pack version number.
3. Delete the Windows 2000 Service Pack n sub-key.
Another folder that gets created when you install a Windows 2000 Service Pack is %SystemRoot%\ServicePackFiles. This is the folder that contains all the new service packs files and allows you to change the state (install / uninstall) Windows components, as described in tip 2914 » A Windows 2000 Service Pack does NOT have to be reinstalled when you change System State?
In tip 2509 » I want to change the location where Windows 2000 expects to find Service Packs, I explained that the location of the service pack files is stored in the ServicePackSourcePath value name, and can be on a network share. This last point should be emphasized. With the possible exception of portable computers, you can save considerable disk space by pointing all clients to the appropriate network share.