How to wipe harddrive with Windows Millenium using command prompt?

I have a laptop with Windows Millenium on it. I want to wipe the hole harddrive windows as well. I have tryed using command prompt "format c:" then clicking Y but says in use so cant do the format anyways round this? i have also tryed FDISK but didnt do anything. Anyone have a quide or tips how i can do this?

You will need to boot from your Windows ME program CD. During this time it will prompt you to format the HD.

boot into safe mode and then DOS prompt only then use the format C:\ command

Get any windows cd (windows XP, winme, win2000) and boot from that cd..Then follow setups and there will be an option to erase everything on the disk (format).