function image() {
};

image = new image();
number = 0;

// imageArray
image[number++] = "<img src='catalog/images/side_slides/slide1.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide2.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide3.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide4.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide5.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide6.jpg' border='0'>"
image[number++] = "<img src='catalog/images/side_slides/slide7.jpg' border='0'>"
// keep adding items here...

increment = Math.floor(Math.random() * number);

document.write(image[increment]);