IPChains/IPTables for 2.4.9 on Slack 8.0

Does anyone know a quick-and-dirty way to configure either ipchains or iptables to keep 1 subnet (192.168.2.x) from accessing another subnet (192.168.2.x) on a peer-to-peer network, while still allowing internet access thru a DSL router? I’m running kernel 2.4.9 on Slackware 8.0 and using that box as a firewall/router/Samba fileserver. All the clients are running Windows 98/98SE. Any help would be most appreciated.

Kevin Reiter