I'd have thought that RH 7.3 is recent enough
(kernel >= 2.4) to actually use iptables?
Ipchains was the 2.2 kernels firewall, and
It's quite easy to set-up if you take the time
to read the manuals and the other documentation
Or you can just use graphical frontends like
Firestarter or Guard-dog, or pre-fab scripts
as can be found on http://freshmeat.net.
Or search here :}