As far as I know, there is no way to create another account on live cd. If you installed it using the code
Code:
sudo knoppix-installer
, set up all the partitions and everything, and installed it as the default configuration (debian), you would be able to make an new, password protected account. Unfortunately, the only way that I know how to do this is when you install from the live CD, you have to setup the account from the configuration option in the installer.

Just dont tell anyone you did this. Apparently installing knoppix on your HD is blasphmy. I dont know why, though.