This simple problem I'm having seems to be quite common (for me anyways), since out of 4 computers I acquired cheaply, three of them exhibit the same problem.
I boot up knoppix v3.4 (also have tried v3.8) on each computer, and they exhibit the same problem where the ethernet connection does not work, even though knoppix apparently recognizes the network card.
In each case, during the hardware autodetection it says "network device eth0 detected; DHCP broadcasting for IP (Backgrounding)", then KDE boots normally.
HOWEVER once in KDE, there is no network connection, and ifconfig only lists "lo", not the "eth0" device, and "pump -i eth0" results in a pause, then "operation failed".
I have verified that this works with popular ethernet cards that are known to work in a couple other computers of mine (booting off the same exact knoppix v3.4 CD). I have tried 2 popular network cards (3com 3c905b-tx and realtek) that are known to work, and have verified that the driver module DOES load. For example, the realtek NIC (which uses 8139too.o and mii.o) does indeed have those modules loaded by knoppix, as verified with lsmod.
As for the cause, since I've eliminated the NIC and the OS (knoppix liveCD), I it appears to be a hardware issue with the computer itself, which I expect must surely have a workaround in the form of
1) a boottime cheatcode, or
2) changing the way the network driver modules are loaded (specifying parameters?), or
3) some unix command that I am unaware of?
The computers are a 500 MHz HP Vectra, 500 Mhz Dell Optiplex, and 550 MHz clone of unknown manufacturer, which have NO other cards in them. And my computer is connected to a 4 port router.