If you need a simple banner rotator in a center block this is quite easy if you install the Logolinks plugin and put this code in a PHP enabled (with return) static page:
$display .= COM_startBlock(' ');
$display .= phpblock_randomLogos();
$display .= COM_endBlock();
return $display;
Set the Logolinks plugin to show only one logo, disable the normal Logolinks block and use 468x60 px banners. Simple and easy to update!
BTW there's a non breaking space between the (' ') in the first line.