If you followed the steps in tip 785 » What steps should you take before installing SP4?, and understand the following notes, you will be able to remove or partially uninstall SP4.
1. SP4 cannot be completely uninstalled using Control Panel / Add/Remove.
2. SP4 makes permanent changes to the Security Account Database and the Security Subsystem.
The only way to completely remove SP4 is to restore the %SystemRoot% folder and recreate of a new ERD. Run RDISK /S.
When you run the uninstall, SP4 leaves the following 6 files:
The uninstall also fails to restore:
Crypt32.dll, Comctl32.dll, Schannel.dll, Cryptdlg.dll, Pstorerc.dll, Psbase.dll, Pstores.exe, Pstorec.dll, Cryptext.dll, Cryptui.dll, Mssign32.dll, Wintrust.dll, Softpub.dll, Mssip32.dll, Mscat32.dll, Initpki.dll, Cryptnet.dll, Xenroll.dll, Dssig.dll, Sigres.exe, Dssbase.dll, Reaenh.dll (128 bit security only), Rsabase.dll, Certmgr.msc, and Syske.exe.
If you don't have a backup, follow these steps to uninstall SP4.
1. Use Control Panel / Add/Remove and select Windows NT 4.0 Service Pack 4. Click Remove.
NOTE: You could also run $NtServicePackUninstall$\spuninst\Spuninst.exe
2. Use the ERD you created prior to the install to replace the 6 files.
3. Restore your previous $NtServicePackUninstall$ folder.
4. Check the SYSTEM Event Log for Event ID 4353, Source: NTServicePack, Description: Windows NT Service Pack 4 was uninstalled. Restoring Windows NT to Service Pack 3.
5. Create a new ERD by running RDISK /S.