changing smoothwall's root password the easy way :
at splash screen press tab
type in smoothwall single and enter
change root password
doing it with knoppix : (hard way)
mount /dev/hda4 /mnt/hda4
chroot /mnt/hda4 /bin/bash
and you're done
(note - if you're unsure as to which partition to mount, look for the partition with the /bin directory in, and mount that).
Hope this helps - for some reason I could not boot into single-user mode on my smoothy.
note that v3 have an issue with booting into single-user mode, a fix for that is being tested at the moment.