Use you XP OS cd and moot from it.
go to recovery console.
Once in the Recovery console:
1. Select the operating system you wish to fix and type the administrator password.
2. Type expand d:\i386\ntoskrnl.ex_ c:\windows\system32 (here I presume that the CD is in D: and XP is installed in C:\Windows)
3. If it already exists, you will then be prompted if you wish to overwrite the file. Type Y and press <Enter> to overwrite the file.
4. Type "exit" to reboot the computer.