well, there is no root password for ubuntu ,only local user and his/her password
you can reset password using recovery mode option in grub.
*www.psychocats.net/ubuntu/resetpassword
if it is not present ,add the line "rw init=/bin/bash" at the end of grub's kernel /boot/... line by replacing "ro quiet splash" .
anyways first try recovery mode.
oh!I got a link for that too
*ubuntuforums.org/archive/index.php/t-3609.html