When you attempt to install SP1 on Windows XP, you receive a message similar to:
one or more protected files on your computer have been modified.
You will receive this message if you have a modified version of Ntoskrnl.exe, usually provided by 3rd parties to display customized graphics when your computer starts up.
Service Pack 1 contains an updated version of Ntoskrnl.exe, which must be installed with the service pack.
The following programs will cause this condition, but others may exist:
LogonUI Boot Randomizer
If the installer offers to replace the file, respond OK. After the service pack is installed, or if the installer quits:
1. Use Control Panel / Add/Remove Programs to uninstall the 3rd party application.
2. Open a CMD prompt and type:
attrib -r -s -h c:\boot.ini
3. Open c:\boot.ini in Notepad and remove any /KERNEL= switch that may be present.
4. Restart your computer.
5. If the service pack did NOT install, try installing it now.