The Format C: deletes everything on the drive including the OS. That's all you need to do prior to reinstalling Windows from the CD.
Insert the bootdisk and power on the machine. It should boot up to a boot menu. Take the option to "Start With CDRom Support".
Somewhere on the screen at the very end, it tells you what drive letter it has temporarily assigned to the CDRom drive. It will look something like this, "Drive X =MSCD001", where "X" is the drive letter that's been temporarily assigned to your CDRom drive for the install. Make a note of what drive letter it displays. If you don't see that phrase on the screen then you didn't get CD Rom support. Stop and do not go any further since you won't be able to install Windows from CD without CDRom support.
Run a test to be sure you can access the CDRom drive. Do this to test it,
Insert the Windows CD and then at a A:\> prompt see if you can list a directory of the CD. If you can, then your fine. Be sure to replace the letter "X" below with the drive letter that was temporarily assigned to your CDRom drive that you should have made note of earlier.
dir x:
Assuming you were able to list a directory of the Windows CD, remove the CD. Then at this point, once you've formatted the drive, there's no going back. All of the data and programs will be erased from the drive. At an A:\> prompt key in the following,
format c:
When it's done insert your Windows CD. Then key in the following command at the prompt and be sure to change the drive letter, "X", to the drive letter that was temporarily assigned to your CDRom drive that you should have made note of earlier.
X:\setup