Routing for multiple uplinks/providers in FreeBSD

Well i am not going to say much words until i show you how it looks like
so i have attached a picture shows every thing


Well i want help in how to configure BSD to act like a router that Route between A local Area Network - and the Internet Through 2 Differant DSL Lines From 2 ISPsin the same time i want to know the possiblety of Running Squid Web Proxy on that Machine and to Force all Network Computers To pass through the Proxy , without putting the Proxy in the Internet ExplorerBest Regards