ntoskrnl.exe is an application that winxp uses to display that Windows Loading image on bootup. NT OS Kernel.
What you can do is to replace the ntoskrnl.exe in your (most probably) C:\Windows\system32 folder with a working one. I'm not sure if you can get it from the Windows XP CD, or if it's hidden somewhere in the CAB files or whatever, but if you can't find it in Windows XP CD, go to http://www.themesxp.org and click on the Boot Screens link, and look for the original XP ntoskrnl.
This is easier to be done if you have a 2nd harddisk. I'm sure there's another way to do it, without using a harddisk, but I can't help you there. So if you have a 2nd harddisk, boot to that harddisk, and copy over the working ntoskrnl.exe to the system32 folder.
When you reboot your system, your Windows XP should be working fine.
Now, if you only have one harddisk or can't get hold of another harddisk for a while, do this : Boot to Windows XP CD. Run the Setup, and select the Repair option.
Ahakz~. Reinstalling Windows XP is my next best suggestion. Sorry.
ZuL