

Object.prototype.addEvent = function(evtType, func) {
   if (this.addEventListener) {
      this.addEventListener(evtType, func, true);
   } else if (this.attachEvent) { 
      this.attachEvent('on' + evtType, func);
   } else { 
      this['on' + evtType] = func;
   }
}

function SlideShow(slideel, faddingSpeed, stopTime, stopOnMouseOver) {	
	var mouseIsOver = false;
	
	if (stopOnMouseOver) {
		slideel.addEvent('mouseover', function() {
			mouseIsOver = true;
		});

		slideel.addEvent('mouseout', function() {
			mouseIsOver = false;
			self.next();
		});
	}
		
	this.next = function() {
		if (mouseIsOver)
			return;

		this.current.fadeOut();
		this.current = this.current.nextSlide;
		this.current.fadeIn();
	}
	
	function createSlides() {
		var imgs = slideel.getElementsByTagName('img');
		var slides = [];
		
		for (var i = 0; i < imgs.length; i++) {		
			slides[i] = new SlideShowImage(imgs[i], self);
		}
		
		for (var i = 0; i < slides.length; i++) {
			if (i == slides.length - 1)
				slides[i].nextSlide = slides[0];
			else
				slides[i].nextSlide = slides[i + 1];
		}
		
		self.current = 	slides[0];
		slides[0].fadeIn();
		
		function SlideShowImage(img, slideShow) {
			img.style.opacity = '0';
	
			this.fadeIn = function() {
				var i = 0;
				while (++i <= 40) {
					window.setTimeout(function() {
						img.style.opacity = parseFloat(img.style.opacity) + 0.025;
					}, i * faddingSpeed);
				}
				
				window.setTimeout(function() {
					slideShow.next();
				}, 40 * faddingSpeed + stopTime);
			}
	
			this.fadeOut = function() {
				var i = 0;
				while (++i <= 40) {
					window.setTimeout(function() {
						img.style.opacity = parseFloat(img.style.opacity) - 0.025;
					}, i * faddingSpeed);
				}
			}
		}
	}
	
	var self = this;
	createSlides(slideel);
}
Usage example: