Once done, you create the redirection rules like this
protocol: tcp from: internal-network netmask: Interface: Internal network interface to: 0.0.0.0 other ports: 80 interface: any [x] redirect to local port redirection port: 3128
3128 is the default port in squid. You also need a rules that let everything goes. Well, you may not want that. You may want a rule that does some fire-walling, but just to make it work, you need at least something like that
protocol: all from: internal network netmask: internal network netmask interface: internal network interface to: 0.0.0.0 interface: external network interface
Use the linuxconf module squid to edit /etc/squid/squid.conf. Turn on transparent proxying. The rest is fine. Use Linuxconf 1.17r2 to handle squid though. Older version did not support squid 2.x properly.