In your image lines try; target = new (not sure if that syntax is correct but it seems to work)
ex:
$image_html[11] = "<a href="http://www.leetgamers.org"target = new ><img src="/ubbthreads/images/banners/leetness.png" border="0"></a>";
As for centering it depends. I have my banner.inc in the html section of header.php file so it looks like this
<br /><center>Welcome To The Forest</center> <br /><?PHP include "$thispath/includes/banners.inc.php"; ?> <br /><center><b>Quote of the Moment</b></center> <br /><center>"XML is like violence: if it doesn't solve your problem, you aren't using enough of it." - Chris Maden</center> <br />
I would think this would work also
<center>
<?PHP include "$thispath/includes/banners.inc.php"; ?>
</center>
