The question is a little bit long......

System A: Centos 4.4
2 network interfaces:
“eth0” connected to Internet through a router, and IP address 192.168.0.100 is given.
“tz0” is a wireless device which can connect to System B, and it's internal IP address is 11.11.1.1 (which is known by System B)

System B: Centos 4.4
2 network interfaces:
“eth0” with no connection
“tz0” is a wireless device which can connect to System A, and it's internal IP address is 11.11.1.2 (which is known by System A)

Problem:
I want to use System A as a network gateway, or something that can redirect the Internet traffic to System B. For example, System B can browse “www.google.com” without any ethernet cable plugged in its “eth0”.

I was told that I can achive this by doing something to the iptable. And I found a website that has the following:

“> To setup the Firewall/NAT, first enable the IP forwarding, by changing the 0 to a 1 on the net.ipv4.ip_forward line of the /etc/sysctl.conf file.
>
> Then, replace the contents of /etc/sysconfig/iptables with the following:
..........................
”
My question are:
1.I change the net.ipv4.ip_forward's value in sysctl.conf file, but I cannot find the “/etc/sysconfig/iptables”.
2.What change should i make in the iptable if the file is found?

Thank you very much!!

You can just write the iptables rules and then run service iptables save
this action will save all rules to the /etc/sysconfig/iptables file .

thank you!
do you mean I am going to create this "iptable" file?

no need to create the file this will do once running the
service iptables save command

as for net.ipv4.ip_forward this line needs to go in /etc/sysctrl.conf
with a value of 0 ro 1 (net.ipv4.ip_forward=1)