Running a graphical environment as root is generally considered dangerous practice. When you for example do that in KDE/Mandriva, you get a red background as default, to remind you of the dangers. I do it sometimes, but with Knoppix, I have been able to do everything I need either with sudo or becoming root with su in a terminal window. As "local" root, I can also run X applications with root privilieges when I need it for administrative purposes. With LXDE and 6.X, everything works fine for me that way - maybe it is otherwise with KDE. In order to limit the consequences of errors I inadvertently make all the time, I try to work with as low privilieges as possible.

The KNOPPIX LiveCD/DVD provides many applications via its menus when you boot to its GUI desktop(s). But you cannot use them for many necessary functions.
If that had been the case for me, I would certainly have tried to get the distribution setup changed. But it isn't, and I don't think many experience it. For me, there are just a few tasks I get forced to do as root. Irritating enough, but no reason for me to run X as root.

Your subject was: How CAN I add a user to Knoppix V6.2 DVD KDE boot? This solution seems to be running as root, not adding another user. I'll be interested in experiences with adding ordinary users. With the new Knoppix much closer to standard Debian, perhaps that is not so much of a problem as it has been traditionally.