Google returned this. It refers to Mandrake, but I can't see why the Fedora installer wouldn't do the same:
Boot into Linux (preferably using a rescue diskette or CD; possibly using Mandrake's installation CD and switching to VC 2 (the second virtual console on most Linux installation packages is a command prompt).
Then, for each drive you can run fdisk -l like:
fdisk -l /dev/hda fdisk -l /dev/hdb fdisk -l /dev/sda
... etc.
Look for Linux and Linux Swap partitions in each of these listings. On any of them that list a Linux or Linux Swap partition, run fdisk in interactive mode (just leave out the -l option), and delete those partitions.
If you want to wipe out a whole drive (e.g. you don't have any non-Linux stuff on it that you wish to preserve) you can use the 'dd' command with script zeros over all of it, or just the MBR. Here's a couple of example commands:
dd if=/dev/zero of=/dev/hda count=1 bs=512 ## just wipe the MBR dd if=/dev/zero of=/dev/hda ## blank everything!