I had the same problem.
As soon as I configured my ethernet card and had it up and running I configured it:
ifconfig eth0 192.168.0.2
and then I opened a browser and entered the address:
and it prompted me for a username and a password. Set the default (username: admin, password: password) and the modem's configuration page will open.
The way I understand it is that you must set the ethernet card at an address (192.168.0.2) different than the one that has been set for the modem (192.168.0.1).
I hope that was helpful.