What are you trying to do? Are you running from CD or a hd install?
Are you trying to run remote-terminal sessions or just get your card up in knoppix so that you can connect to the internet?
What kind of internet connection do you have?

if you are running in X (graphical mode), start konsole or xterm and use the following command:
sudo ifconfig
here is the output on my computer:
knoppix@1[knoppix]$ sudo ifconfig
eth0 Link encap:Ethernet HWaddr 00:A0:CC:3E:40:4C
inet addr:192.168.1.95 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1212 errors:2 dropped:0 overruns:0 frame:0
TX packets:1245 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:967264 (944.5 KiB) TX bytes:248993 (243.1 KiB)
Interrupt:11 Base address:0x7000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:4 errors:0 dropped:0 overruns:0 frame:0
TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:200 (200.0 b) TX bytes:200 (200.0 b)
The " eth0 " information is about my NIC, I have a couple of rtl8139 cards and they have been set up by knoppix on my systems, but I have a gateway computer that is running a dhcp server so when I run knoppix I get my NIC set up by dhcp on the gateway.

If you don't have an entry for eth0 then run the following command:
sudo modprobe 8139too
if you get error messages here post them back, if you don't get any error messages, then type this command:
sudo netcardconfig
if you have a router you should select dhcp broadcast, if you are using a windows computer for your gateway and are using windows internet connection sharing, you will have to enter the ip address, netmask, network address, gateway and nameserver. Easiest way to find this info is to boot into windows, run winipcfg and from the drop down select your rtl8139 network card, write down all of the above and then put that info in with netcardconfig.

HTH

rock