For OSs earlier than XP, I think you would need to use Eraser 5.7, no longer supported (i.e. we can't necessarily advise if it doesn't work), but available from the Eraser page on Sourceforge. I know that 5.7 works on Windows 95/98, so hope that it works on 2000 also.
Eraser will I believe work with RAID volumes, but what 5.7 can and can't do in this respect I don't know. And erasing everything and then free space can be tricky; it is quite hard to be sure that you've left nothing sensitive behind. Indeed, I am not sure that preserving a Windows 2000 installation makes much sense any more.
Your best bet may be to use DBAN (Darik's Boot and Nuke) to clear the whole drive. There is a companion forum to this one, and also a rather more active forum and downloads on Sourceforge. Essentially, the software is a floppy disk or CD image, from which you create a boot disk. You boot with this disk, and, if DBAN works, it makes everything stored on the machine non-recoverable. The real issue with DBAN is that it hasn't been supported or updated for some years, and the basic OS from which it runs does not work with all hardware.
With such old hardware, I know of no entirely foolproof method of doing what you want. But both Eraser 5.7 and DBAN (it's your choice) may be worth a go.