I have installed tproxy patch(kernel and squid) and it is working...
squid uses the client ip address in its requests.

I haven't changed anything special in iptables, I have a rule in
iptables doing the redirect of port 80 to 3128 and it's working.

and I need nat working to access the internet but nat is not working
properly :\

the requests made by squid bypass nat and go to the internet with lan
ip addresses

I tried a ping to google.com and it's works... so I thing the problem
is only with squid requests :\
does anyone know where can I find the problem?