Su is for root, but in ubuntu for secerity reasons it is sudo. If you run like
Gentoo it would be Sudo. In other Linux O/S is it "yum" and it can be confusing
to all hell on what is what.
It sounds like maybe the drive is not mounted all proper. Did Ubuntu mount
automatic?
http://www.psychocats.net/ubuntu/mountlinux
http://ubuntuforums.org/showthread.php?t=409952
Of course if you are not getting the answers here. I would highly recommend on
Ubuntu forums.
http://ubuntuforums.org