I did have dual nic issues which I now have sloved but now I can't figure out how to share the connection. I do know that I need IPTables, an DNS/DHCP server and dual network crads. I have dnsmasq and dhcpd installed but I have no clue how to get them to work and I also have iptables which, to me is as equally confusing.
Also last time I tried to configure and have run Iptables and the DNS/DHCP server nothing would run right on my computer (except for my ADSL connection), KDE and GNOME and PWM (not enlightenment) would all stall in startup and most things won't open and firefox would crash every five seconds. So to say the least I am going to reinstall Arch . (sorry if I ask too many questions just trying to learn!)
I think you need to set up your box as a router.
You need the iproute/iptables packages.
I'm not a network guru so I don't know how to set up all this. Make sure your NICS are correctly recognized before setting anything up.