get a domain content and the position of a specific size div, for instance 300x250

I would like for testing purpose to get the content of a specific domain (http://ift.tt/rsXarK eg), get the position of a specific div size, let's say 300x250. Once, i get such info about the div size position into a given page, i would like to change the content of that div with something else, in my case the script of a banner. how can i achieve this?
i was thinking to get the content of the page using curl and later i would place the tag into the page. can you help me with some working example? Cheers A.