At the boot prompt try:
knoppix nodhcp

If you get past it and it boots try from a root prompt:

ifconfig and if eth0 is up try
pump -i eth0

if eth0 is not up try
ifconfig eth0 up and then try
pump -i eth0

If that doesn't work then you ethernet card is probably not supported. You might want to try a newer versoin of KNOPPIX.

Good luck!

Mike