Here is how I finally did it:

One must edit /etc/X11/XF86Config-4 file. This must be done as a root of course. Then do the following:

1) in section "ServerLayout" add the line:
InputDevice "Synaptics" "AlwaysCore"

2) in section "Module" add the line:
Load "synaptics"

3) create the following section:
Section "InputDevice"
Identifier "Synaptics"
Driver "synaptics"
Option "TouchpadOff" "1"
EndSection

To keep this setting when computer is rebooted one must save configuration. In KDE manager choose KNOPPIX->Configure->"Save KNOPPIX Configuration"

Then next time when Knoppix is started one should type "knoppix myconfig=...." to restore this configuration.

Thanks angor, it looks like your suggestion was more or less like this.