Linux 2.2 kernels will not have iptables (no official patches as yet). Though I will give examples for both ipchains and iptables, I would suggest you to start using iptables because of the greater flexibility and the reasons as explained above. With iptables, you can do stateful comparision of packets and also have enhanced set of rules. If you have a very old system with low memory (<8MB), suggest you to use only ipchains. Iptables keeps the states in RAM and may need a little more memory.
On 2.4 kernels, you may run either ipchains or iptables but not both at the same time. The rules specified by ipchains have precedence and the kernel even first attempts to load ipchains first. If you have ipchains modules installed, iptables may never start automatically.
If you decide to use iptables, you have a choice of several user interfaces for configuring your own firewall rules later-on. You may use knetfilter (GUI based), gshield, ferm, AGT or MM-Firewall. If you decide to use ipchains, you have a GUI tool gnome-lokkit to do the firewall configuration for your future firewall needs.