what do you think the best firewall is for slakware 7
almost all Linux distributions come with ipchains compiled into the kernel, just read man ipchains to get an idea of how to setup a firewall, however is you are still unsure, there are firewall scripts out there, just download them, try them and after that learn how to configure your own firewall
Ex. Godot's Firewall Script.
Im sure the slackware that you installed also came with Firewall installed in. Check the man page for the Firewall.