configuring IPFW in FreeBSD

I have problems in setting up the firewall in our
gateway.We 8 machines connected in our LAN and these clients connect to the internet through this gateway running ADSL connection.
But whenever I run my ruleset of IPFW,LAN is disconnected to the internet.My gateway is running Freebsd 4.5 and the clients are win 98 machine.
I can ping from the client to the gateway and vice versa but browsing or sending e-mail is not possible from the client.

Thanks