The Views Slideshow module makes the process of creating a slideshow in Drupal extremely easy, but I've always found one important feature to be missing: a fullscreen setting.
Here is a script that take a slide image (or any HTML element for that matter) and set it to be the size of the viewer's browser window (preserving the aspect ratio). This works with single elements or a set of elements. It's particularly useful if you'd like to set an image to be the background of a given page-- this will ensure that the image always covers the entire viewport.
I'd recommend dropping this code into a resize.js file located in your Drupal theme's folder. From there, just add the filename to your theme's .info file, and it will be loaded into every page of your site (if that's what you're going for).
Be sure to set the 'slides' variable to the appropriate target element, and you should be all set!