The sudo program in Kubuntu says may root password is wrong but I entered the correct password and re-intastalled the operating system. P.S. I use Kubuntu 5.10 Breezy Badger
Now It still says I have a wrong password even though I tried to enter all my accounts passwords!
sudo does not ask you for your root password, it asks for the password of the user who calls it. For example, if your regular user is bob and you type sudo, it will ask for bob's password.
There is no root password by default in Ubuntu/Kubuntu because the root account is disabled.