An alternative way to install - where no manual intervention is required is to have a common '/boot' partition for all OSes - this way there is also a common /boot/grub/grub.conf.
So, if you update FC3 kernel - the correct grub.conf is updated. And if you update RHL9 kernel - the correct grub.conf is updated.
Wouldn't this cause problems:
1. because there would have to be two "template" boot entries, one for each OS, and grubby might have trouble figuring out which one to use?
2. because FC3 might want to use SELinux labels, which RH9 wouldn't support?
A similar approach I thought of, which would also have these problems, would be to mount the FC3 /boot partition on (say) /fc3boot and make the RH9 /boot/grub/grub.conf a symlink to /fc3boot/grub/grub.conf
Paul.