Can't access router's IP address

Hi,

I just got my ADSL connection and the phone company provided me with an ECI ADSL router/modem. I can browse the net without problems, but I can't access the router's IP address in order to enable/configure the firewall. The phone company told me that the configuration they provided me with doesn't allow me to configure the firewall (great!). Right now I'm using the OS X (10.2.8) firewall and a demo of NetBarrier, but I'd like to be able to use the router's built-in firewall and save the expense of buying NetBarrier. Any suggestions for what I should do to access the IP address? Do I need to disable NetBarrier first? Or should I just buy NetBarrier and feel secure with that? Thanks.

Claire