You didn't download the English version, so you have the German version right?
Do you have German menus in KDE as well?
OK, different question: what do you get if you type
ifconfig -a into a terminal?
Is there a line that starts with eth0?
Because if there isn't such a line, chances are that KNOPPIX doesn't recognize your network card.
If there is a line starting with eth0, you probably just need to set it up correctly.
Did you already run the network card configuration wizard? (the program to set your ip address etc.)?
If no: I'll tell you how to do it.
If yes: hm... I hope you don't say yes, because then the problem might be more complex....