This will not rotate them but display a random one on each page view:
PHP Code:
<?php $random_number = rand(1,3);
switch ($random_number) {
case 1: $img = "someimage1.gif"; $link = "http://advertiser1.com/"; break;
case 2: $img = "someimage2.gif"; $link = "http://advertiser2.com/"; break;
case 3: $img = "someimage3.gif"; $link = "http://advertiser3.com/";
} ?>
<a href="<?php echo $link; ?>"><img src="<?php echo $img; ?>" alt="" /></a>
If you want real rotation, specific view shares per advertiser and other settings look for an ad management script or plugin