Windows root\system32\ntoskrnl.exe is missing or corrupt

I need some help. I'm getting this message on another user's PC. Some other
posts related to this suggest going to support.microsoft.com/kb/314477 and
following the directions. The problem I have is that I don't have the option
of pressing the "R" key to access the recovery console. I've tried booting up
in safe mode and safe mode with command prompt. I continue to get the same
message. Surely I don't have to format and reload Windows?! The XP disc that
I have is an older one from the SP1 days. That probably explains why I don't
have the option of pressing the "R" key. Service pack 2 has been installed.

Any help would be greatly appreciated.