#!/bin/sh
iptables -F INPUT
iptables -F FORWARD
iptables -F OUTPUT
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A PREROUTING  --in-interface eth0 --destination ! 192.168.0.0/24 -p tcp -m multiport --dport 80 -j DNAT --to 192.168.0.1:3128

Bad argument `192.168.0.0/24'

 ifconfig
eth0      Link encap:Ethernet  HWaddr 00:1b:11:79:3c:e5
          inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::21b:11ff:fe79:3ce5/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1443 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2613 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:280594 (274.0 KiB)  TX bytes:570339 (556.9 KiB)
          Interrupt:16

eth1      Link encap:Ethernet  HWaddr 00:40:f4:ea:5a:11
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::240:f4ff:feea:5a11/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:19971159 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16426216 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:372525562 (355.2 MiB)  TX bytes:2972513385 (2.7 GiB)
          Interrupt:20 Base address:0xd000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:7324 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7324 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1800281 (1.7 MiB)  TX bytes:1800281 (1.7 MiB)