banner code

I have a site where members can submit their banner to be displayed on a surfing page the problem is the banners wont rotate only one banner is shown. As i know almost nothing about php i was hoping someone could point me in the right direction, i think the fault lies with this bit of code.

<?
if ($banner_info[banner_url] == "")
{
echo "<div align=right>No banner to display</div>";
}
else
{
?>

<div align="right"><a href="<? echo $conf[site_url] ?>redirect.php?id=<? echo $banner_info[id] ?>" target="_blank"><img src="<? echo $banner_info[banner_url] ?>" height="60"></a></div>
<?
}
?>

Thanking you in advance
Zalka

 

you should post the variables meanings too for us to get a help-hand!