I'd Windows 7(sda1) and Ubuntu 11.04(sda6) on my laptop. Ubuntu's grub was installed on MBR. Then I installed Fedora 15(sda2). But by mistake I installed Fedora's grub on MBR. Due to this Ubuntu's grub deleted from MBR. Now while booting I can see only Fedora and Windows option on grub.
I've edited Fedora's grub.conf as
title Ubuntu rootnoverify (hd0,5) chainloader +1
But no use of it.. (I think I need to recover stage 1 of Ubuntu's grub.)
How do I edit grub.conf of Fedora to get Ubuntu back in boot list?
You should be able to use Fedora's grub just fine. I don't think you can use the chainloader option unless you have Ubuntu's grub installed to the boot partition of the Ubuntu install (You say it was installed to the MBR before the Fedora installation)
You will need to find out which partitions contain your Ubuntu filesystems, and create a custom menuentry similar to the ones you see for Fedora.
Once you can boot into Ubuntu, you might want to re-install Ubuntu's grub to the MBR. I believe it will detect the Fedora installation automagically, where your Fedora installation is failing to detect Ubuntu.