If you don't like Javascript you could use this PHP solution:
1. Create a folder called rand_images and put all the images in it.
2. Name the images 0.gif, 1.gif, 2.gif, 3.gif, 4.gif etc.
3. Create a file called rand_images.php and put this code into it:
><?
// This script returns an image
header("Content-type: image/gif");
$image_count = 5; // Set this variable to the total amount of
// images in the rand_images folder
// Load a random image
$image = fopen("rand_images/".rand(0,$image_count-1).".gif","r");
// Return the image
fpassthru($image);
?>
4. Now when you want to display a random image, just use this html code:
><img src="rand_images.php">
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This should work