Walker,
There are two solutions for your problem. The first one you can find here by "Method 4":
http://forums.spybot.info/blog.php?b=14
and the second one is described below. Please decide by yourself which variant is best for you:
An easy way to solve the problem is to use the repair installation function on your windows 2000 installation disk (you need a valid Windows 2000 key):
1. Insert the installation disk into your cd/dvd drive
2. Make sure that the boot sequence in the bios is set to "boot from cd first"
3. Start your computer and you will see the dialog "press any key to boot from cd..." please do so
4. Your computer will load a lot of stuff. When he is finished you have to choose
"To set up Windows 2000 now, press ENTER" (in the following steps you will get the possibility to repair your current windows automatically)
5. In the next step you have to confirm the Licensing Agreement by pressing "F8"
6. The computer should search for versions of Win2000 already installed on the computer. Afterwards you can choose to repair the old Windows 2000 on your system by pressing "r"
Then Windows will copy all necessary system files to your computer. Additionally it will replace all necessary registry keys and when the installation is finished you can login to the computer.
Attention: Maybe not all third-party software installed on your system will work without problems. Perhaps you have to reinstall some of these software. But all your files located on the harddisk should be available again.