dual boot (RHEL3 and RHEL4) problem: need guidance to edit grub.conf in MBR
 

I currently have a system with a 40G hard drive that has been partitioned RHEL4 (18G) and RHEL3(18G) and 4G free space on its hard drive. I installed RHEL4 first and everything was fine. Upon successfully installing RHEL3 I believe that I "overrode" the initial grub.conf file and now only RHEL3 (the last installed) is present in the grub menu. Upon researching this problem I have been advised mount the system with universal grub.conf file from the just installed system. Where does the universal grub.conf reside (boot/grub/grub.conf)? And how do in get it into access the other partition (hd0)? Are there alternative ways to do this that may be easier and will not required me to reinstalled both OS's. Thanks. This is my first time going this. Thanks.

Questions:
How exactly are both versions of RHEL installed??

Does each version of RHEL have a /boot directory which has files and the grub sub-directory??

What is the output from the typed command; /sbin/fdisk -l