I have a linux pc with 2 network cards in it. They both work, and i would like to share a cable internet connection with my other XP computer. This is my network:

cable internet -> (eth0) Linux machine (eth1)- > XP machine

now, i'm able to ping my xp machine no prob, and i have internet on my linux machine too. I used the "medium" firewall config when i first installed red hat 9. And I modified my iptables like this:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -d 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -s ! 10.0.0.0/24 -j DROP

I got this config from a redhat 8 book. I saved this config and restarted but i still don't have internet on my xp machine yet.

The ip addresses of my machines are: 10.0.0.10 (linux), 10.0.0.2 (xp)

What should i do? Am i missing something?

Any help would be appreciated.

Try enabling packet forwarding:
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/ip_dynaddr

If that doesn't work then try flushig nyour iptables and load your rules again:
iptables -F
iptables -F -t nat
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -d 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -s ! 10.0.0.0/24 -j DROP