I have a sony vista home laptop here that will not boot. It stops at a screen that says ntoskrnl.exe is missing or corupt.
I made the system repair CD (No dvd was supplied with the laptop) and went though and repaired the error. (also ran full chkdsk with no errors found)
The system comes back pre SP1 (No idea if it was SP1 before or not, the guy did not know)
If any windows updates are applied, (Even one or two and NOT SP1) then the system reverts back to the same unbootable state.