Custom Script for Responsive Wordpress Thumbnails

I need something similar to what is happening at [login to view URL] or [login to view URL] to work in with the WordPress theme I am building on the [login to view URL] responsive css framework. unlike the above 2 references, I'd like to swap between 4 different sized images: mobile-sized tablet/small desktop-sized widescreen-sized huge monitor-sized (the end client works on 30" monitors) since WordPress already resizes any uploaded image into thumbnail, medium and large sizes (with the ability to add more featured image sizes), i'd like a custom script that works with (or is similar to) the_post_thumbnail() so that it will progressively load the appropriate size. for example, mobile browsers should load the smallest image like the_post_thumbnail('thumbnail') while the widescreen would load the_post_thumbnail('large') like the above 2 links, it should also dynamically change on browser resize.