Routing packets with IPTABLES?

["Reginald NALLARATNAM" <regi@toolsnottoys.com>]

Hello,

Hardware Layout:
   Firewall #1: (Linux Box)
    I have a linux box with 2 nics.
   eth1 @ 192.168.20.1  
   eth0 @ 192.168.30.2 
   Gateway:  192.168.30.1  

   Firewall # 2: (Some other router)
   interface 1:  192.168.20.2
   interface 2:  192.168.30.2
   Gateway:  192.168.30.1  

   Web server:
   192.168.20.100
   Gateway:  192.168.20.2 (Firewall # 2)   

   Gateway - is someother Firewall/Router that allows both firewall #1 and #2 to connect to the internet.
   192.168.30.1

Question:
   Is there a way to route incomming packets from the gateway to eth0 on firewall #1 based on source IP and destination Port to the web server @ 192.168.20.100?
The only way this will work if Firewall # 1 routes or forwards the packets to web server without connection tracking, since the return answer from web server will go through firewall # 2.

Could some give me an example or the command to do this using iptables, if not how else can this be done?

Thanks in advance.