In order to format your drive you will need a windows format utility. This utility is found in the Windows boot disks. If you have a floppy drive you can simply download a Windows 98 boot disk for free at www.bootdisk.com
That will make a bootable floppy disk for you. You can also creat a bootable Windows 98 CD but you will still need the floppy to create the bootable CD.
Lets say you downloaded the Windows98 boot disk and created the floppy.
Once you do that, all you have to do is restart your computer and put the floppy in the A:
During the booting process, the computer will boot from the files on that floppy disk.
After all is said and done, you will be in a DOS prompt (A:\)
Just type Format C:
and hit enter. You will be asked if you're sure a few times, just hit Y for yes and it will proceed to the format process.