Hi there, thanks for posting the solution to your boggle.
I had a Fedora install with LVM and couldn't access the files until I used your instructions on my Jaunty 9.04 desktop with the LVM drive attached via usb.
Two things; firstly I couldn't depmod dm_mod - I got a module not found error although this did not impact my success.
Secondly to unmount the drive I had to use the -l switch on the umount command:
FATAL: Module dm_mod not found.
otherwise the unmount failed due to a process or user accessing it.
sudo umount -l /media/root