Going back to the recovery scenario...
Run the redhat installer, but instead of hitting enter at the first prompt, type "linux rescue"
Follow the steps, and have the system attempt to discover and mount your system as /mnt/sysimage
If it can't to that DON'T PANIC. Drop to the prompt, and mount the partition:
mount /dev/hda? /mnt/sysimage
Once you have that
If you have a seperate boot partition:
mount /dev/hda? /boot
Now we re-install the bootloader. I'm assuming you are using GRUB:
Variables: X - the partion number where your BOOT partion lives - 1
(if your boot partion is /dev/hda1 X=0)
(inside grub program)
(Assuming of course your OS is on the master of the primary controller.)
More detailed instruction can be found on the gentoo installation guide: