Why do you try to setup your modem, if it worked in FC-1 then it will work with FC-3.
If your modem is connected to eth0 then you only worry about the hardware setup / installation of your Ethernet interface (on-board).
99% of all ADSL modems that connect with Ethernet use a HTML setup.
For some more information about FC-3 and an Ethernet ADSL modem/router look at http://adsl.yoll.net/setting-up-adsl...-08-Linux.html
With kind regards