Hello There,,,
I would like to say that I am a newbie too...but I'm getting better...

I not sure how to configure your knoppix to use the cable modem...I would think that it would have configured itself right away..but is it seeing your NIC cards?

if it is you can go under control center in kde and click on network and then lan browsing and try to use the auto configure ( ResLISa daemon) that might work.. is your DHCP brocast on?

The easiest thing that I found is to have a router between the modem and computer... then it just kind of picks it up right away....Did you use the shell terminal and type ifconfig eth0 up or ifconfig eth1 up? I hope that this will help you if not you can contact me maybe and tell me more information about your system..!

I am online most the time... my msn is [email protected] and my icq is 212554643 :P