Let us go through the initial steps. Boot from the 1st CD of RHEL. Type
at the boot prompt. When it asks you to try to mount already installed distribution, coose yes. If it went successful it will tell you that the existing installation is mounted under "/mnt/sysimage"
to chroot in to it.
From here you have 2 options:
1. Install GRUB to hard disk
Here I assume your hard disk is /dev/hda. If it's different, replace it with yours.
2. Install GRUB to a floppy
Not now, John!
gives you more information about the disk creating. See it also. Remember your paths may vary.
For more information try searching in Google Linux Search