Wifi Setup

Hi,
I have a couple of questions about my wifi setup.  I am planning on 
setting up free hotspots and using ads and banners to generate my
revenue. I want the users connected to my wireless network see the banners/ads 
on any sites that they visit (the upper 10% of the page is dedicated to 
ads/banners and the rest of the page is dedicated for the site. For example, if 
the user hits cnn.com, the top 10% of the page is the ads/banner and the bottom 
90% is cnn's site.My first question is how do I achieve this?

The second question is we are going to deploy access points in certain area of 
the city and they will all collapse in one central location.  What do I need to 
secure this network?

Any advices or links to related articles would be helpful and appreciated.  
Thanks in advance..

Ferno

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