I've now amended the page so that the adverts will be occluded by the main page if your screen resolution or window is too small to show both.
I've tested it with Mozilla Firefox and Internet Explorer.
By the way, if you use IE, er.. don't. It's full of security holes and 'features' that spyware and malware can exploit.
Firefox is free (it's a variant of Mozilla), plus it's one of the fastest, safest browsers there is. I work for a financial institution, and we're not even allowed to use IE - we use Firefox!
http://www.mozilla.org/products/firefox/