Hi,
First thing is do a backup, copy files that you want to save into a safe place, maybe make a directory in /myth for storage. Write down the hostname!
Just do a manual install and when it ask where to put the boot loader mark PARTITION. When it finishes, it will exit you to a prompt. do an ls /boot and write down the vmlinuz-2.6.1x-chw-x (replace x with your numbers) Reboot
At the grub menu, you can manually edit your KM link or just open up Ubuntu and edit the /boot/grub/menu.lst (as sudo) Fix the numbers using the info that you just wrote down at install
When you boot into the R5E50, it will not know that you have a /myth partition so you have to go through most of the setup stuff. I simply esc out of the two setup screens but do answer the other questions properly.
Once the myth mainmenu comes up, open an xterm and fix /etc/fstab to be /myth and remove the no from noauto. Mine looks like this:
/dev/hda8 /myth ext3 auto,users,exec 0 0
Once the fstab is right , check the hostname. If it isn't right, things aren't happy and KM doesn't even know what language you use.
# mount /myth
# mythrestore
# reboot
Should only need your personnel special tweaks
Mike