I have had such a problem, too.
After installing Knoppix in debian-style the system started with gnome. The network-admin found here did not function, it hangs.
Try to change to KDE and use the knoppix-networkcard-setup.
Or do the configuring by hand in /etc/network/interfaces.

auto eth0
iface eth0 inet dhcp

Or perhaps

auto eth0 eth1
iface eth0 inet dhcp
iface eth1 inet dhcp

into this file.

This does only function if you have a dhcp-server. In other cases you need to specify the ip-adress, and gateway-adress.