proxy server

Hello all, this is actually my first post, so here it goes

i want my desktop pc to act as a proxy server for the rest of my lan network, in other way to share my internet connection
it goes something like this:

DSL router --> Desktop PC --> lan network

the desktop pc connects to the dsl router only by wireless (wlan0) and to the rest of the
lan network with a wired card (eth0)
the wifi is using the ndiswrapper driver
here is the script i tried:

#!/bin/sh
iwconfig essid "blahblah"
iwconfig key s:blahblahblah
ifconfig wlan0 up
dhclient3 wlan0
ifconfig eth0 up
ifconfig eth0 192.168.0.1
INTIF="eth0"
EXTIF="wlan0"
EXTIP="`/sbin/ifconfig wlan0 | grep 'inet addr' | awk '{print $2}' | sed -e 's/.*://'`"
/sbin/depmod -a
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe ip_conntrack_irc
/sbin/modprobe iptable_nat
/sbin/modprobe ip_nat_ftp
echo "1" > /proc/sys/net/ipv4/ip_forward
echo "1" > /proc/sys/net/ipv4/ip_dynaddr
iptables -P INPUT ACCEPT
iptables -F INPUT
iptables -P OUTPUT ACCEPT
iptables -F OUTPUT
iptables -P FORWARD DROP
iptables -F FORWARD
iptables -t nat -F
iptables -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
iptables -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE

one more weird thing is that when i'm connected to the internet (with the wlan0 interface) and i'm giving to eth0 the ip 192.168.0.1 i cannot ping anything from internet, e.g Google but i can still ping the dsl router.

any help will be grateful. thenx :>