you downloaded the iptables from source? you mean you downloaded the iptables source package? why would you go to that length? with Slackware 10.2, you get it by default or if you didn't, you can install it from the cd itself.
AFAIK there is a rc.firewall script in /etc/rc.d/, you just need to make it non-executable.
Code:
chmod 644 /etc/rc.d/rc.firewall
to flush a running iptables rules, you would do a
basically you can re-write the rc.firewall script such that it switches between start|stop|restart just like in sysv type linuses. Have a look over some redhat system firewall scripts and such. or if you want total, unload the iptables module currently loaded.