here is my setup:
I have one windows xp machine that runs ics (connected through dialup, and has an eithernet card connected to the gentoo box) and my gentoo box is routed through it, and attached to the gentoo box over a serial cable (null modem) wtih slip (slattach) is an old laptop without a nic, i can see the internet with the gentoo box fine, but i wish to be able to have the delilinux box (old laptop) be able to access the internet as well through it's null modem connection. i have fooled around with iptables and such and tried
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
but that only comes back and says
iptables: Invalid argument
i was thinking it would be the same as trying to say, have a dsl modem attached to the eth0 on a linux box, and have eth1 share internet to the rest of the network, except wtih eth0 connected to the windows machine, and sl0 connected to the delilinux, but i cant seme to make it work. the delilinux box will ping to and fro with the gentoo box fine, and gentoo box will ping to and fro with windows xp box, but i cant make delilinux ping windows, nor anything else outside the gentoo/delilinux link.
can someone give me some detailed information on how this should all be set up?
thanks
-ox

do you have ip forwarding enabled ?

check if /proc/sys/net/ipv4/ip_forward = 1

also, if you are using nat through static connection (eth0), i think you will need -j SNAT instead of MASQUERADE.

i had /proc/sys/net/ipv4/ip_forward set to 1, and i tired the -j SNAT option instead of MASQUERADE but it didn't seem to make much differance, now after messing with it for a while i have screwed something up and everytime i start iptables i cant get to anything like there is a rule blocking everything, i tired to flush it wtih -F but it did'nt seem to make much differance, and iptables -L (or iptables -t nat -L) dont show antyhing in there.