Basically I know I can get things to filter out banner ads and pop-up ads to compliment squid. But I will need something to do the opposite. What I need is when people get on these free wifi hotspots I own and go to a website it will go through squid running transparently. When the website returns the response I want squid to insert the banner ad (eventually randomized banner ads) at the top of the page then send it off to the laptop that requested the page. Why you may ask? And can't people just block it you may ask? Well to answer the first question, as this network get's much bigger running costs for the network will grow because more bandwidth will be needed so I will have to bring in some sponsers. To answer the second question, yes I know these can be easily block but most people (windows users) are dunce and never even thought about looking for something to block them, and the few that can good for them they'll have free internet with no hitches.

Thanks alot in advanced guys (gals?)!

well, since you own the wireless network and give out IP addresses using only DHCP, set the gateway to the linux box running squid so that they can't get out to the internet directly. Set up a firewall on the linux box.

Search for "squid transparent proxy" on google. Note that https is not possible.

For modifying response to the client, I don;t think it can be done without writing an add on to squid. Post a question to squid-cache.org mailing list and Henrik will suggest a solution for sure.