Actually, I just found out we run PHP 4.0.6... Will the query string/GET process still work? Right now it's not and I thought I saw in the docs that the POST/GET isn't in pre 4.1...
Just add some Javascript to the links around your thumbnails, like this:
<a href="javascript:window.open('show_photo.php?img=image.jpg');">
Then you need to create a script called show_photo.php that takes the "img"
var passed by the Javascript above and loads that image onto the page.
$image = $_GET['img'];
echo "<img src='$image' border=0>";
Hope that helps.
Monty