Installed 9.10 (from the same DVD) on two different systems here, same issue.
I created a user, say it's "foo", on the initial install. When I set it to log in automatically it works fine but "sudo <cmd>" prompts for the password and it always fails after "[sudo] password for foo:" as if I am typing in the wrong password (I am not).
If I try and log out and log back in, it won't do the graphical login, says "Authentication Failure".
I have reinstalled about half a dozen times across two different systems, figuring I must have really typoed the password when installing and therefore I must be typing in a wrong password. But after doing this over, and over, and over, it seems clear that I am not actually typing in the wrong password. It's just broken.
Same thing for the GUI synaptic update manager (tells me there are updates available, I try and update, it asks for the password, then tells me "Authentication Failure").
Incidentally, if I do "passwd" and change it from the shell, if I type the [correct] password, then try and change it to the current password, it says "Password Unchanged". So clearly somewhere something knows the right password.
This is a huge PITA since you can't do a freakin' thing on Ubuntu without sudo working.
So what am I doing wrong, or what can I do differently to make this work?