If you use the default location for operating system files in windows 2000 pro which of the following files does the pc need
the Ntldr file, the Autoexec.bat file, the Boot.ini file or the config.sys file

Yes, all of them! Well, I'm not sure about the Config.sys actually but it does need the others.

Update: Yes, the Config.sys is a Windows 2000 file although I know that, in earlier versions of Windows, you could delete it if you didn't have an application or device that added a reference into it. I wouldn't mess about with these files at all in Windows 2000 to be honest though - too much of a headache when you reboot your system and it says you've broken Windows.