FC3 "read only file system" after Ubuntu install

[Duncan Lithgow]

I just installed Ubuntu - I was careful (I think) and created a
'/boot', '/home' and '/' for it. Ubuntu starts fine. I did not install
grub to the MBR (as you can see it has it's own partition).

Now when I try and start FC3 it gets to 

'/var/lock/subsystem/kudzu': read only file system
starting system logger:

a fair sized pause, and then a list of things which are read only -
which of course means it can't start and hangs.

The only possible cause I found was something about having two '/'
partitions being a problem - fair enough I guess. I then found this
(unresolved) possible solution at
http://forums.fedoraforum.org/showthread.php?t=32977

---
I am pretty certain that the problem you are running into is that BOTH
the FC3 disk, and the previously "mirrored" disk both have a partition
"labeled" as "/" (root).
...
you can avoid this by either changing the "/etc/fstab" root device to
use a physical device instead of the partition label.

To boot FC3, with two partitions labeled as "/" (root), you have to
explicitly tell the grub bootloader which one to use. At the "grub"
boot menu, hit the "a" key for "appending" to the kernel boot line.
Then add "root=/dev/whateveryourrootpartitionishere" to the end of the
kernel parameters line.

You can will then have to relabel one or the other of the two
partitions that are labeled as "/" (root), and update your
"/etc/fstab" accordingly.
---

I don't understand this, and don't know how to do it. Can anyone help?

What I do know how to do is:
- start in rescue mode and navigate from the command line
I don't know:
- how to edit and save using vi

Thanks, Duncan