There is nothing you can do in your html that will force this "extended description" to happen. It's something that the Google algorithm decides on, and its display is based on your site's popularity as measured by PR and possibly traffic.
What you can do is first ensure a clear and well labeled site structure so that such links are possible - and then get links, PR and traffic.
At this point, it is a Google question, rather than an HTML question, so I refer you to the Google Search forum. Here are some threads on the topic: