you don't need ipchains (or the newer/better iptables) in your kernel or modules to do routing.
However, as soon as you want to do more than pure routing (select WHAT to route, i.e. firewalling) you need either iptables or ipchains.
Since you still have an old 2.2 kernel you'll have to go with ipchains.
first make sure that your box is in effect routing the trafic, and not just listening on both eths.
Code:
cat /proc/sys/net/ipv4/ip_forward
if it sais 0, you're not forwarding (routing). to correct this, do
Code:
echo 1 > /proc/sys/net/ipv4/ip_forward
And probably add this to your start-up scripts.
I can't help you with the ipchains setup (since I only know iptables)