How about posting for us all the output of the command 'ifconfig' so we can see what's what there.
It may or may not help ME help you, but it will help somebody help you.

output of ifconfig:

eth0 Lien encap:UNSPEC HWaddr 00-00-0A-E6-FF-44-AE-13-00-00-00-00-00-00-00-00
inet adr:192.168.0.2 Bcast:192.168.0.255 Masque:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:1990 errors:48 dropped:48 overruns:0 carrier:0
collisions:0 lg file transmission:1000
RX bytes:0 (0.0 b) TX bytes:108798 (106.2 KiB)

eth1 Lien encap:Ethernet HWaddr 00:02:E3:09:3C:82
inet adr:192.168.1.53 Bcast:192.168.1.255 Masque:255.255.255.0
adr inet6: fe80::202:e3ff:fe09:3c82/64 Scope:Lien
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:29281 errors:3 dropped:0 overruns:0 frame:0
TX packets:26376 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 lg file transmission:1000
RX bytes:17407329 (16.6 MiB) TX bytes:6503352 (6.2 MiB)
Interruption:169 Adresse de base:0xde00

eth2 Lien encap:Ethernet HWaddr 00:14:2A:63:EA:A8
adr inet6: fe80::214:2aff:fe63:eaa8/64 Scope:Lien
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:15 errors:0 dropped:0 overruns:0 frame:0
TX packets:100 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 lg file transmission:1000
RX bytes:900 (900.0 b) TX bytes:13778 (13.4 KiB)
Interruption:193 Adresse de base:0x8000

lo Lien encap:Boucle locale
inet adr:127.0.0.1 Masque:255.0.0.0
adr inet6: ::1/128 Scope:Hôte
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:17773 errors:0 dropped:0 overruns:0 frame:0
TX packets:17773 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 lg file transmission:0
RX bytes:890860 (869.9 KiB) TX bytes:890860 (869.9 KiB)

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:

http://192.168.0.1

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.