aggiungi queste 3 variabili
(comunque lo script non e' fatto bene: non si espone tutto cosi' a livello di window, jquery ha un sistema per estendersi via plugin decisamente evoluto)

$autoplay=true;
$autoplayTimer = 5000;
$autoplayTimeout=false;

e le parti in rosso
codice:
			function BackgroundLoad($this,imageWidth,imageHeight,imgSrc){
				$this.fadeOut("fast",function(){
					$this.attr("src", "").attr("src", imgSrc); //change image source
					FullScreenBackground($this,imageWidth,imageHeight); //scale background image
					$preloader.fadeOut("fast",function(){$this.fadeIn("slow");});
					var imageTitle=$img_title.data("imageTitle");
					if(imageTitle){
						$this.attr("alt", imageTitle).attr("title", imageTitle);
						$img_title.fadeOut("fast",function(){
							$img_title.html(imageTitle).fadeIn();
						});
					} else {
						$img_title.fadeOut("fast",function(){
							$img_title.html($this.attr("title")).fadeIn();
						});
					}
					if($autoplay) autoplayStart() 
				});
			}
			
			function autoplayStart(){
				if($autoplayTimeout) clearTimeout($autoplayTimeout)
				if($autoplay) $autoplayTimeout=setTimeout(function(){$nextImageBtn.trigger('click')},$autoplayTimer)
			}
chiaramente $autoplay e' un booleano che puoi usare qualora volessi aggiungere all' interfaccia un play/pause

ciao