I searched around the interwebs but couldn’t find a single, comprehensive resource on how to setup a world material for Cycles that combines the best of both worlds, i.e. a high resolution backplate with hdri lighting, without requiring an enormous amount of ram. In the end I pieced all stuff together and wrote a small blog article, with explanations and sample node setups, including info on where to position the camera and how to rotate the backplate and environment lighting in a synchronized way:
http://blenderthings.blogspot.com/2012/12/how-to-set-up-simple-hdri-environment.html
(with thanks to all sorts of scattered sources around the web).
cheers