make a dos boot disc with the format command on it and fdisk command aswell

boot from this disk then when u get a command prompt type "fdisk c:\" without the "" bits tho. follow the instructions and then format the disk - the lot is wiped

or if you want to do a really nasty format, go into the bios menu and do a "low level format" on the disk - altho this is only reccomended if thereeare failed sectors and clusters on the drive.

best o luck