ntoskrnl.exe missing at bootup

I had the following config of OS on my PC:
C: Win XP sp2 (root)
D: XP 64bit 2003 edition
E: longhorn on my PC.
C: accidently got formatted & xpsp2 reinstalled: I edited the new MBR to show the other distros…When I try to load the other OSs via OS select menu at boot,I get the message “ntoskrnl.exe missing:reinstall a copy of it”.So I did a copy-paste from the windows installation CD to whatever folders of the other OSs that were analogous folders to those in XPsp2.But that didn’t help.When I try to repair the distros via the intallation CDs,I end up working in Caldera OS that I’m not familiar with.Plz help me out without having to format it again.Also how do we “uninstall” an OS??I mean without having to format the drive….