I don't have any code at the moment for the project I am about to start, but it would be something as simple as this:
<img src="images/file.jpg" width="100%">
This I would sit inside a responsive div, or just have it sitting on the page by itself outside of any div. It works fine on any devices I have tried it in, and it also works fine in any browser I have tried, but I have been told that IE doesn't hold the aspect ratio, but I've not seen it, and as the majority of the world are in IE, I feel it is still best to build for it... no matter how much it gripes me!
Matthew, the first place to begin would be to create a new document in DW as 'Fluid Grid Layout (FGL)' in DW CS6. Pluralist site is a responsive site, exactly what you can achieve with DW CS6.
This 3 part tutorial is a great place to start - http://webdesign.tutsplus.com/series/dreamweaver-cs6-fluid-grids/
All the best!