1. Open command.com in your Windows XP/2000 Install.
2. Go to the root of your C: drive (as defined in your Windows XP/2000 Install).
3. Key in cd boot to navigate to the boot directory.
4. Key in fixntfs -xp -all and hit enter.
5. Reboot.

Optional Step: If you're really cautious, or just want to be entirely Longhorn-free, grab your XP/2000 Installation CD and copy ntldr and ntdetect.com to your C: drive and overwrite the originals.

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There you go, your original XP/2000 Boot sector is restored!

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