It's not too difficult but sadly not as easy as changing 800px to 80%
The easy part is the css to change the width of BgContainer, Container, Header, Navigation, Layout & Footer. The tricky part is making the curved background images work with a variable width theme, you'll need to chop the images up and add some extra markup.
I sopke to a friend who is a web-designer. He said will do it in a couple of days as soon as he found some free time. Will be great help. I will post the converted theme on the site so that others may also benefit from it.