The iptables command and the Linux kernel combined is of the best firewalls in existence.
I could not understand what you asking. Write a little bit clearer you have run-ons spanning 6 lines-it's pretty hard to read. You don't have to right in perfect sentences. Just make it eye friendly and not in one block. I'm not being offensive.
For possibility 1 of what I think your saying:
I infer that you cannot connect to ports on your slackware box. Then you need to tell the daemons that you want to use what port(s) to listen on, and setup proper authentication with those daemons. Tell your firewall to allow access from the SAME-HOST, the machine your protecting with the firewall.
For possibility 2 of what I think your saying:
You still can connect to ports on your slackware machine even though you think firewalled everything. You can comment out everything in /etc/inetd.conf and /etc/services. Your xserver may be listening on port 6000, tell it to stop that. Then if you 'nmap -v -sS -sU localhost -p 1-65535' you'll see that all ports on your machine are closed.
Also you may configure your /etc/hosts.deny and /etc/host.allow files to deny all connections by default, then nothing can connect to certain daemons on your box.
But if you want some real fire power, use iptables.
Did I get what you were saying?