There are a couple of ways to fix this, but the easiest is to run a repair from the Windows 2000 CD.
Pop it in and boot from it. It will look like it's starting a new install, but it isnt. Wait for it to load up the initial files, and you will see an option to hit R for repair. Do this and select the automatic repair option. Don't worry about not having Emergency Repair Disks, just continue through the choices.
This wont harm your original data.