Ok I see what you want. What you must do is apply a prerouting rule to do a DNAT on packets incoming the LAN interface with a destination of the publick IP address. Try the following one:
iptables -t nat -I PREROUTING -p tcp -d 126.96.36.199 --dport 80 -i ETH00 -j DNAT --to-destination 192.168.1.1:80
188.8.131.52 is your public IP address
192.168.1.1 is the internal IP address of the server
ETH00 is the LAN interface. In this example I am forwarding the http (tcp/80) port.