I have faced the same or similar problem. Using ADSL router and only one netcard. Knoppix 3.8.1 found two interfaces: eth0 and eth1. Shouldn't it find only one? As a result, I'd never knew which one to set. First of all I've chose eth0 and no DHCP. It worked fine but, after booting, got stucked and couldn't even ping any address.

Thanks.