[Synov_son]

var nav = function(max){
	this.max = max;
	this.current = this.current || -1;
	this.next = function(){
        this.current = this.current < this.max - 1 ? this.current + 1 : 0;
		this.slide(this.current)
    };
	this.prev = function(){
        this.current = this.current > 0 ? this.current - 1 : this.max - 1;
		this.slide(this.current)
    };
	this.slide = function(current){
		$('#slideshow img').fadeOut(1500, 'easeOutQuart');
		$('#slideshow #thumbs span').removeClass('active');
		$('#slideshow #thumbs span#'+current).addClass('active');
		$('#slideshow img#'+current).fadeIn(1500, 'easeOutQuart');
	}
};
var slider = new nav($('#slideshow img').length);
	slider.next()

Вот так вроде и должно, но только первый блок выцветает