If you just want to change the default window manager, but not the details of how this window manager is called, you can look for the following lines in /etc/init.d/knoppix-autoconfig:

Code:
case "$DESKTOP" in kde|wmaker|gnome|xfce|icewm|twm) ;; *) DESKTOP="kde"; ;; esac
(I reconstructed from my own changed file, so it might be slightly different on the original.)
This checks if the user has specified a value for desktop at the boot prompt. If this value is one of the option in the list kde,wmaker,gnome etc, it will keep that value. Otherwise, it will use kde. If you change 'kde' (in DESKTOP="kde"), you change the default window manager. You can also delete options that you deinstalled (or want to disable at the boot prompt for some reason).