Presumably you're going to install a fresh copy of w2k after the format?
If so, just insert the w2k CD, restart computer (making sure that in BIOS, CDROM comes before the hard disk in boot sequence or boot device).
If asked to "press any key to boot from CD", just press any key on keyboard.
You'll enter w2k Setup.
Follow the prompts, remembering that the option you want is always to install a fresh copy of w2k (and not to repair by reinstalling).
You will ultimately be asked where to install w2k, and shown the partitions on your hard disk.
Use the up/down arrows to highlight the C partition.
If you're happy with sticking with the existing size of the C partition, just press Enter to install a fresh copy of w2k on that partition.
You'll be warned about losing existing Windows. Just confirm what you want to do.
When you are presented with the formatting options, select "Format with NTFS" or "Format with FAT", whichever you prefer (preferably NTFS).
Do not select "Leave existing file system intact".
Then w2k Setup will start formatting the disk.
After formatting, installation will continue by copying files to your hard disk.
It will then reboot. Leave your CD in, but this time let it boot from the hard disk (that is, do NOT press any key to boot from CD).
Follow the prompts. When all is done, it will reboot into w2k proper.