See
this post for lots of people that have done this. Just connect LAN2 to a spare port on your router.
You need to make sure your router uses the
192.168.1.0/24 subnet and that
192.168.1.1 is not already in use... If your router is not on the
192.168.1.0/24 subnet change the IP address of the modem. If
192.168.1.1 is in use (i.e. by your router), change the modem IP address to an alternate one.