ZA and PC tools firewalls do not work on my system they just try to mess it up, so I will have a look at Jettico 
I tried a Jetico 2 beta (don't remember which one) & it froze my computer. Jetico 2 is still in beta, maybe you will have a better experience.
Jetico 1, I believe is the best firewall. Uses between 1 & just under 9mb of RAM, depending on how much you've got running on your system. It usually ran at the lower end of the spectrum for me.
I'm now using PC Tools Firewall Plus because Jetico 1 can't be set for MS updates. I had to be at the keyboard to allow each & every MS update & each & every MS update install. MS updates are no problem with PCTFW+.