Squid proxy on Centos 5

I’ve got squid running on centos 5.I can browse the internet from the proxy server itself but i cant do so from my LAN client machines. They’re all configured to go through this proxy server i.e. proxy address and port number is set in the browser. I have also set up an authentication program: auth_param basic program. But with all this in place, I cant seen to have access to the internet from these LAN client machines.