Ok, let's see, if you're lucky, U have another copy f the file in your own Windows. If not, in your xp cd. But U still need the cd, from wherever you copy. And do you know how to use cmd?
Boot from xp cd. (F2 or del to enter bios)
Change boot order so that cd ro boots first.
Restart and press R for recovery console
Welcome to recovery console! (I just like saying that, just ignore me! )
Press 1, press enter or type password.
You will need to backup(just rename the extension) of the Ntoskrnl.exe file located in C:\Windows\System32
Then copy the one from cd or your own computer to C:\Windows\System32.
ren C:\windows\system32\ntoskrnl.exe ntoskrnl.old
then U can search if there is another ntoskrnl in your pc , or U can copy the one from the xp cd, using the expand command.
expand d:\i386\ntoskrnl.ex_ c:\windows\system32
Restart. if this doesn't work ,you have to copy 4 files the same way U did with this one from the Windows\Repair folder to the System32\config\ . But only if the previous doesn't work.
If it opens , U can copy your personal files , and do a clean install if U want, but if everything is fine and working properly, then U don't need to to do that. (this depends on the version of Ntoskrnl you got, and the one U copy)