I was able to fix this problem with the bigpond cable login client as follows, so that I can use knoppix from the cdrom. While the debian version installs various things to /usr/sbin etc, that wasn't necessary.

I fixed this as follows:

compile bpalogin-2.0.2 and save into your home dir - probably save to you hard disk by knoppix.
edit the conf file with correct user name
simply run ./bpalogin -c /home/knoppix/bpa/bpalogin-2.0.2/bpalogin.conf
or wherever your conf file is (somewhere easier perhaps?)
And she works!