Sorry, I don't run fedora, but when you boot up do you get a grub / lilo boot loader so you can choose which OS etc you want to load?
If so, then you can type a 3 before you choose to boot Fedora.
Otherwise, your other option is to use a live cd and mount your root partition and edit from there. I suggest Knoppix or damnsmalllinux.
mount -t vfat /dev/hda1 /mnt/rescue (substitute correct filesystem)
adjust to your needs.