You could boot a linux livecd and do something like Code: dd if=/dev/zero of=/dev/hda
This is not formatting (though), it will just leave your disk completely plain, without partitions. Beware that this will overwrite your whole drive with zeroes, which means that you will not be able to recover a single bit out of it once this has finished. If you do this, make sure you choose the correct drive and don't throw /dev/hda in there blindingly.
However, there shouldn't be a need for that. If you truly want to erase all the partitions you should be able to do it from almost any installer. And if not, just boot a livecd, and then use fdisk, parted, gparted or whatever suits you to delete all the partitions. Save, reboot and insert whatever installation disk you want. |