Resize Image based on Browser Window Size

What I would like to do is have the images resize based on the browser size. I am trying to make them fill 100%. I’m not sure how to do this, I tried using width:auto and no height attribute because I do still want them to keep their proportions. I also tried some javascript code that I found as well as many google search results. I’m all out of ideas.
I’m using a jquery slider that resizes the slider based on the largest image size it loads. If I can resize the images before the slider load’s them, this should accomplish what I want.

To see what i’m working with, http://konceptj.com/clients/nathan/

Any idea’s you have would be greatly appreciated, if you can even just point me in the right direction I would take that too

See this previous thread for some possible answers.

I have a small resizing demo here but its pretty basic but does contain a little logic to handle image dimensions.