I've been trying to do something similar but was not able to succeed. I was using Fedora Core 6 since few months and wanted to use Ubuntu. After installing Ubuntu, I was not able to boot FC6 since then. Now I've no idea what is the problem and where is the problem. I hope someone can help me out on this.
My Grub screen shot is below:
================================================================================
title Ubuntu, kernel 2.6.17-11-generic
root (hd0,8)
kernel /boot/vmlinuz-2.6.17-11-generic root=/dev/sda9 ro quiet splash
initrd /boot/initrd.img-2.6.17-11-generic
quiet
savedefault
boot
title Ubuntu, kernel 2.6.17-11-generic (recovery mode)
root (hd0,8)
kernel /boot/vmlinuz-2.6.17-11-generic root=/dev/sda9 ro single
initrd /boot/initrd.img-2.6.17-11-generic
boot
title Ubuntu, memtest86+
root (hd0,8)
kernel /boot/memtest86+.bin
quiet
boot
### END DEBIAN AUTOMAGIC KERNELS LIST
# This is a divider, added to separate the menu items below from the Debian
# ones.
title Fedora Core 6:
root (hd0,7)
kernel /boot/vmlinuz-2.6.18-1.2798.fc6 root=/dev/sda7
initrd /boot/initrd.2.6.18-1.2798.fc6.img
savedefault
boot
# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/sda2
title Microsoft Windows XP Home Edition
root (hd0,1)
savedefault
makeactive
chainloader +1
======================================================================
Maybe this will also help, the fdisk screen shot, where FC6 was on /dev/sda7.
Disk /dev/sda: 100.0 GB, 100030242816 bytes
255 heads, 63 sectors/track, 12161 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 12 96358+ de Dell Utility
/dev/sda2 * 13 2951 23607517+ 7 HPFS/NTFS
/dev/sda3 2952 11769 70830585 f W95 Ext'd (LBA)
/dev/sda4 11770 12161 3148740 c W95 FAT32 (LBA)
/dev/sda5 2952 5891 23615518+ 7 HPFS/NTFS
/dev/sda6 5892 8831 23615518+ 7 HPFS/NTFS
/dev/sda7 10464 10476 104391 83 Linux
/dev/sda8 10477 11769 10385991 8e Linux LVM
/dev/sda9 8855 10202 10827778+ 83 Linux
/dev/sda10 10203 10463 2096451 82 Linux swap / Solaris
========================================================================
Any help/suggestion in this regard will be appreciated!