RH Linux 7.3, 2.4 Kernel

I am trying to force all of my LAN users to go through a SQUID (2.4Stable1) proxy I have setup. And I thought I would be able to use iptables to deny services to all asking for PORT 80 or 8080 for web browsing. They should be using SQUID (certain IP, certain port # given) for that.

For all other ports, I would only allow certain IP addresses or certain MAC addresses to go through.

1. Can I force (allowable MAC or IPs) to use proxy (SQUID) for web browsing?

2. For non-web browsing activities, can I also restrict non-allowed MAC or IPs?

Please give me or point me towards some specific examples on these two tasks if you would. Thanks