Help implementing Supersized.js in Drupal 7
There are a few issues here. 


It's not in Drupal best practices to add a script to html.tpl.php 
That being said, there are two ways to do it. (a) You can add it to your theme's .info file and call a .js file script from there (i.e. "scripts.js") in your theme folder, ideally in a "js" or "scripts" sub-folder if you need this site-wide (b)  If you don't need it site-wide or you can call it with drupal_add_js in your theme's template.php file to target only specific pages / paths
The way Javascript gets called has changed in Drupal 7


The main new thing is to include something like:

(function ($) {
//needed for drupal 7
Drupal.behaviors.myTheme = {
attach: function(context, settings) {
// end drupal 7 syntax


... at the top of your script. 

so a clean version should work like so:

(function ($) {

//needed for drupal 7
Drupal.behaviors.myTheme = {
attach: function(context, settings) {
// end dtupal 7 syntax


            $.supersized({

                //Functionality
                slideshow               :   1,      //Slideshow on/off
                autoplay                :   1,      //Slideshow starts playing automatically
                start_slide             :   1,      //Start slide (0 is random)
                random                  :   0,      //Randomize slide order (Ignores start slide)
                slide_interval          :   3000,   //Length between transitions
                transition              :   1,      //0-None, 1-Fade, 2-Slide Top, 3-Slide Right, 4-Slide Bottom, 5-Slide Left, 6-Carousel Right, 7-Carousel Left
                transition_speed        :   500,    //Speed of transition
                new_window              :   1,      //Image links open in new window/tab
                pause_hover             :   0,      //Pause slideshow on hover
                keyboard_nav            :   1,      //Keyboard navigation on/off
                performance             :   1,      //0-Normal, 1-Hybrid speed/quality, 2-Optimizes image quality, 3-Optimizes transition speed // (Only works for Firefox/IE, not Webkit)
                image_protect           :   1,      //Disables image dragging and right click with Javascript
                image_path              :   'img/', //Default image path

                //Size &amp; Position
                min_width               :   0,      //Min width allowed (in pixels)
                min_height              :   0,      //Min height allowed (in pixels)
                vertical_center         :   1,      //Vertically center background
                horizontal_center       :   1,      //Horizontally center background
                fit_portrait            :   1,      //Portrait images will not exceed browser height
                fit_landscape           :   0,      //Landscape images will not exceed browser width

                //Components
                navigation              :   1,      //Slideshow controls on/off
                thumbnail_navigation    :   1,      //Thumbnail navigation
                slide_counter           :   1,      //Display slide numbers
                slide_captions          :   1,      //Slide caption (Pull from "title" in slides array)
                slides                  :   [       //Slideshow Images
                                                    {image : 'http://buildinternet.s3.amazonaws.com/projects/supersized/3.1/slides/quietchaos-kitty.jpg', title : 'Quiet Chaos by Kitty Gallannaugh', url : 'http://www.nonsensesociety.com/2010/12/kitty-gallannaugh/'},  
                                                    {image : 'http://buildinternet.s3.amazonaws.com/projects/supersized/3.1/slides/wanderers-kitty.jpg', title : 'Wanderers by Kitty Gallannaugh', url : 'http://www.nonsensesociety.com/2010/12/kitty-gallannaugh/'},  
                                                    {image : 'http://buildinternet.s3.amazonaws.com/projects/supersized/3.1/slides/apple-kitty.jpg', title : 'Applewood by Kitty Gallannaugh', url : 'http://www.nonsensesociety.com/2010/12/kitty-gallannaugh/'}  
                                            ]

            }); 

//ending drupal 7 specific calls / syntax
}};
}) (jQuery);