How did they do this?

Hi, please excuse me for posting in the wrong area …

Please look at this site; Denver.org and then the picture.

I want to know how they were able to move from page to page …

Is it all Java? Can I use ASP.net? Or even asp.net AJAX?

I’m not looking for any code, just some name / term dropping so I can super Google the hell out of it … if you can provide more; blog articles, examples, whatever you can afford, please do so. Thank you.