i have a ubuntu server which i want to use as a transparent proxy, (i have no issue setting up squid, just the iptables. The server only has one network interface. The server sits on the same subnet as the router which is the current gateway to the internet for clients, i want to simply set the gateway on the clients pointing at the transparent proxy which in turn forwards the requests to the router and off to the internet. See me diagram, can anybody offer to help with the iptables configuration to achieve this scenario?

subnet mask /22

     Router(10.4.12.1)         Transparent Proxy (eth0, 10.4.12.2)
       |                   |
  +----+----+---------+----+----+
  |         |         |         |
Comp1(10.4.12.6)     Comp2(10.4.12.5)     Comp3(10.4.12.4)     Comp4(10.4.12.3)

Thanks