Try the username that use selected when you installed Kubuntu. The password is the same as the username.
I have tried that (after installing 1.1 RC1) but it won't accept it, not with the password the same as the username, nor with the password I set for the account under Kubuntu.
It keeps saying "Invalid username or password, please try again".
And it's not like I don't know the username of the only account on the system. I suppose I could dig for that forum post that shows how to reset this in the DB, but I would rather like to know what I'm doing wrong here.