Your root password is what you enter as administrator password, asked when you install knoppix.

To add user, log as root and run this command : adduser
To delete user : deluser <username>
To change password: passwd

Did kdm appear when you boot? It won't appear if you install using knoppix-style hdd instalL
If there is no kdm, read my post:
http://www.knoppix.net/forum/viewtop...r=asc&start=10