I assume that your /boot partition is properly formatted (i.e. ext2/ext3)
Boot a knoppix bootdisk, mount your partitions in the way you usually would, e.g.
# assuming you have only a root partition and boot partition
# mount root (/) partition
mount /dev/hdxy /mnt/hdxy
# mount boot partition in proper place:
mount /dev/hduv /mnt/hdxy/boot
# find out what the kernel rpm is called
rpm -q kernel
rpm --reinstall kernel-foo.rpm
# (something like the above)
Repeat last two lines for the grub package. I think that's all that resides in /boot, so after doing a grub install from the grub shell (unless grub is still installed and properly set up), everything should be back to normal (sign out, unmount, take knoppix out and reboot).