You should probably explain that you want the function of the site, not the topic.
And I will explain again in case I wasn't clear before: this is not just your basic modifying of HTML. That site has a server-side script, the source of which can't be viewed. It is probably just some very simple PHP, and with a little googling I can probably remember how to parse a URL in PHP and place it into the iframe src tag, but I'm just not interested enough to try. Sorry.
Last, but not least, your goal here seems to be to make money with ads, but this type of site will surely violate Google's Adsense terms.
If you still want to move forward, put in your ad that you need a script that takes an arbitrary URL (which is appended to your own URL) and places it into an iframe. You also need to overlay an image, which will be hidden to start, that will unhide after a given period of time.