How to install ubuntu 8.04 on a system already having RHEL 5
 

Hi guys....
I have RHEL 5 and Windows already installed on my system.I tried to install the latest ubuntu 8.04 desktop sdition alongside these.I made a 7.5 GB partition and 512 MB swap separate frm windows and RHEL occupied space.In the installation too everything went well.I enabled the ubuntu to install its boot loader in (hd0).Everything was fine till now.
The problem came when I rebooted.I found that RHEL GRUB menu came as usual on the screen as if nothing happened.There was no ubuntu boot loader.Also there in the menu showed no option for Ubuntu.
Kindly can anyone plz give a step-by-step solution??
( Plzlist exactly what to add in /boot/grub/menu.lst of RHEL 5 if any )

You need to add information for your Ubuntu to your /boot/grub/grub.conf on Fedora. Presumably this already has your Fedora and Windows boot information in it so you should be able to model your Ubuntu information based on what you see for those.

Boot into RHEL and open a terminal, issue command: fdisk -l to see which partition is which.

For example:
If RHEL /boot or root partition (RHEL usually makes a separate /boot partition...I think) is /dev/hda2 issue the four commands below as root to put you in a grub session, tell grub to use the RHEL configuration file, and install itself in the MBR of the first drive.
Reboot.
Make sure you use the right partition. If you make a mistake and things go whacky, boot with the Ubuntu live CD in a live session and try again.

Grub counts from 0, so hda2 becomes hd0,1 to grub.

Thanx a lot junior hacker for u'r detailed response.But,after setup (hd0) it gave an error.

Well I tried various combinations of modifications to /boot/grub/grub.conf of RHEL too but to no avail..
my ubuntu was installed on /dev/sda12 and fter sum time I realised that it corresponds to (hd0,11) when I found the boot folder of ubuntu using "find" in grub command line,as it seems grub starts counting from 0.

I added a lot of stuff...

Well at last I noticed that my boot loader was in a separate partition.maybe due desperation,I decided to overwrite it with ubuntu grub.
I re-installed ubuntu twice then
1)once it overwrote that partition (/dev/sda8 of size abt 101 MB with 15 MB occupied)by making it the /boot and on re-start got a black grub> prompt.I panicked on dat as I m nt very conversant with it.
2)I re-installed with default /hd0 option.

Now,I have ubuntu 8.04 running alongside Windows XP but hav a new Problem - the boot loader now doesn't detect RHEL 5.

Can any1 offer a solution?

/dev/hd0?

Newer kernels map even the ide drives as /dev/sd devices instead of /dev/hd. Perhaps your issue is the drive is being seen as /dev/sd0 in the RHEL installation but as /dev/hd0 in the Ubuntu installation.

What version of kernel does the Ubuntu one have. RHEL5 definitely uses the later 2.6 kernel that see /dev/sd instead of /dev/hd for both SCSI and IDE drives.