Are you starting from scratch with an unused, unformatted hard driver, or is it a drive that is currently being used and you just want to erase the data from? The first one is more complicated, so I'll explain that.
Using a boot disk if you are on Windows 9x or Me, boot into DOS with CD-ROM support (if you want to use your CD-ROM) and type in "fdisk." This will take you into a program where you can choose how you want to partition the disk and whether to set it up as FAT16 or FAT32.
Once this is completed, you will need to restart the computer and keep the boot disk in so you can go back to DOS.
Now type in format c: (if you are formatting the c🙂 and press enter. It will prompt you to make sure and once you do that, just sit back and wait.
All in all, a pretty simple procedure.