Please.. I need help.

I have a problem with setting up my iptables.
I need to forward port 80 and other useful ports to my local machine.
Aside from port forwarding, i also configured NAT for other PCs in my local
network to access the internet. NAT works fine except for my port forward.
I just get confused because other ports being forwarded works just fine. e.g
port 25(stmp) but just can't forward port 80. I think the problem is with the
return packets that is forwarded back into my server.

Below is the complete script running in my linux box... please help. there should be something wrong with my script.


#Load NAT module

modprobe ip_tables

modprobe ip_conntrack
modprobe iptable_nat

modprobe ip_conntrack_ftp
modprobe ip_nat_ftp

#Turn IP Forward
sysctl -w net.ipv4.ip_forward=1

iptables -t nat -F POSTROUTING

# Add Iptables nat to eth0 (local loop back)
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

iptables -t nat -F PREROUTING
iptables -t nat -F OUTPUT

#forward http port

iptables -t nat -A PREROUTING -p tcp --dport 80 -i eth0 -j DNAT --to-destination

#forward other ports for mail
iptables -t nat -A PREROUTING -p tcp --dport 25 -i eth0 -j DNAT --to-destination
iptables -t nat -A PREROUTING -p tcp --dport 443 -i eth0 -j DNAT --to-destination
iptables -t nat -A PREROUTING -p tcp --dport 1352 -i eth0 -j DNAT --to-destination

# Flush forward chain
iptables -F FORWARD

iptables -A FORWARD -s -j ACCEPT
iptables -A FORWARD -d -j ACCEPT

#set drop rules
# All access

iptables -A FORWARD -m mac --mac-source 00:02:55:07:47:03 -j ACCEPT #ibmserver
iptables -A FORWARD -m mac --mac-source 00:04:75:C7:61:69 -j ACCEPT #Access_server

# Deny everyone else

iptables -A FORWARD -s -j DROP

Thank You for replying