A. As was explained in "Q. Important steps for installing Service Pack 4.", Service Pack 4 makes some changes to registry which can't be undone. Because of this, in the event of a Service Pack 4 uninstall the following files are left unrestored

• samsrv.dll
• samlib.dll
• winlogon.exe
• lsasrv.dll
• services.exe
• msv1_0.dll

Additionally the files below are also not restored:

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.

To uninstall the Service Pack either start the Add/Remove programs control panel applet (Start - Settings - Control Panel - Add/Remove programs), select "Windows NT Service Pack 4" and click Remove, or, move to the %systemroot%\$NtServicePackUninstall$\spuninst directory and run spuninst.exe.

If you wanted to completely uninstall the service pack, undoing the registry changes and restoring all original files you would need to restore the %systemroot% directory from a back and repair the registry using the ERD disk you created. Alternatively you could uninstall as normal then use the ERD to repair the registry and replace the six files that the uninstall does not fix.