Hi tr,
I think you're right, and that is, I need something like in kiosk mode.

As follow what you say I think that it isn't a Knoppix-distro issue, but maybe an app itself issue. I've noticed as example that qtparted has the same xvidtune rights in knoppix, "-rwxr-xr-x 1 root root". But even having 'others' the execute permission qtparted ask me simple non_root user for root passwd while xvidtune no. Isn't a general unix/linux policy that only root can manage hardware settings?

best regards, max.