<?php
$banner1 = '<a href="Banner1_URL" target="_blank"><img src="Banner1_IMG_SRC" alt="Banner1_ALT" />></a>';
$banner2 = '<a href="Banner2_URL" target="_blank"><img src="Banner2_IMG_SRC" alt="Banner2_ALT" title="Banner2_TITLE"></a>';
$banner3 = '<a href="Banner3_URL" target="_blank"><img src="Banner3_IMG_SRC" alt="Banner3_ALT" title="Banner3_TITLE"></a>';
$banner4 = '<a href="Banner4_URL" target="_blank"><img src="Banner4_IMG_SRC" alt="Banner4_ALT" title="Banner4_TITLE"></a>';
$banners = array($banner1, $banner2, $banner3, $banner4);
shuffle($banners);
?>
To display random banner, include the above PHP creating the banner image array, and then simply drop the print $banners[0] function into your document:
<div>
<h1>Simple Image Banner Rotator</h1>
<?php print $banners[0] ?>
</div?>
?>