Formatting causes you to loose all data on your computers hard disk drive
Check out
www.bootdisk.com and find the Windows 2000 boot disk.
Put it onto a floppy, and then start the boot disk, and type:
format C: /s /q
for a quick format (just deletes the data)
format C: /s
does a complete format (Recommended)
You will need the Windows 2000 disk to reinstall Windows though, there is no way around this.