function image() {
};

image = new image();
number = 0;

// imageArray
image[number++] = "<img src='images/guc_041.jpg' width='289' height='162' border='0'>"
image[number++] = "<img src='images/guc_042.jpg' width='289' height='162' border='0'>"
image[number++] = "<img src='images/guc_043.jpg' width='289' height='162' border='0'>"
image[number++] = "<img src='images/guc_044.jpg' width='289' height='162' border='0'>"
image[number++] = "<img src='images/guc_045.jpg' width='289' height='162' border='0'>"

// keep adding items here...

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

document.write(image[increment]);