I'm sorry for the mistake, but I forgot something...
I also have a Wireless PCI card! So, the on-board Ethernet card is disabled correctly afterall... :P
Therefore, my configuration is this one...
eth0 - Gigabyte WPKG PCI WLAN Card
eth1 - Realtek RTL8139 Fast Ethernet NIC
eth2 - nForce4 built-in Gbit MAC (Marvell 88E1111 PHY)
Anyway, I did what you said ("sudo pump -i eth1") and it worked fine!
Thanks man!

When I run KWiFiManager, it shows Interface eth0, so that's my wireless PCI card...
But when I start the Network card configuration tool (netcardconfig) and select:
> "eth0 Netzwerkkart_0" (small translation error here!!!)
> "Use DHCP broadcast?" (and click "Yes")
It shows this message and then it completelly locks up Knoppix like on the boot sequence...
Sending DHCP broadcast from device eth0
When I boot normally, the 2 messages that appear are:
Network device eth0 detected, DHCP broadcasting for IP.
Network device eth1 detected, DHCP broadcasting for IP._
And then it locks up... So I though the problem was on the eth1 card, but it's in fact on eth0...
It's some sort of problem when getting the IP address from the Wireless card, that shouldn't be happening...

Still... it's kind of annoying having to type that "knoppix nodhcp" command everytime I want to boot Knoppix...
Will this problem be fixed on next versions?
If you'd like, just tell me what I have to do and I can try to help you discover a solution for this!