Here u go !! This is from M$
Microsoft Knowledge Base Article - 327101
Error message: Windows has detected that one or more protected core system files (kernel) on your computer have been modified
This article was previously published under Q327101
SYMPTOMS
When you try to install Windows XP Service Pack 1 (SP1), you may receive the following error message:
Windows has detected that one or more protected core system files
(kernel) on your computer have been modified. The Service Pack contains updated versions of those files, which work to provide a stable environment for your programs. Due to this modification, the Service Pack will not be installed. For more information, see Knowledge Base article Q327101 at
http://support.microsoft.com.
CAUSE
This behavior may occur if your computer has a modified version of the Ntoskrnl.exe file that uses the /KERNEL switch in the Boot.ini file. This condition may exist because your computer has a third-party program installed that customizes the graphics that are displayed when your computer starts up. Third-party programs that can cause this condition include the following:
bootXP
LogonUI Boot Randomizer
RESOLUTION
To resolve this problem, follow these steps:
Click OK to close the error message.
Click Start, click Run, and then type appwiz.cpl in the Open box.
Click the program that customizes the startup graphics, and then click Remove.
Restart your computer, and then try to install SP1 again. If the problem persists, go to step 5.
On the desktop, right-click My Computer, and then click Properties.
Click the Advanced tab, and then click Settings under Startup and Recovery.
Under System Startup, click Edit.
The Boot.ini file opens in Notepad.
Locate and then delete the /KERNEL= switch.
Save and then close the Boot.ini file.
Restart your computer.
Try to install Windows XP SP1.
NOTE: After you complete the steps to resolve the problem, SP1 should install correctly. However, if your computer is running a modified Ntoskrnl.exe file, you may receive a message when you try to install SP1 that states that the SP1 setup program will replace the modified Ntoskrnl.exe file with an updated version.
STATUS
This behavior is by design.
MORE INFORMATION
For additional information about this issue, click the following article number to view the article in the Microsoft Knowledge Base:
327120 Error Message: Windows Service Pack 1 Has Detected That One or More Protected Core System Files on Your Computer Have Been Modified
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.
here the link:
http://support.microsoft.com/default...b;en-us;327101