I have setup something similer for our network, using RouterOS 3.10 and Squid 2.7
I hope you find this info helpful as i had a lot of support from this forum to get it working.
Here is the RouterOS 3.10 Config for forwarding port 80 traffic to squid.
Look in the IP->Firewall section for details.
Here is my squid config file. I am using squid 2.7 on ubuntu-8.04.1-desktop-i386
http://www.rednetwifi.com/images/squid% ... 20file.txt
i am happy to help if i can but i am a newbie too..
email me at darren(at)rednetwifi.com or skypeme at rednetwifics