Sorry Alonso i forgot i said that i would put the code up... now for the code you will need.
For this method you wil have to put it into:
[file.jpg = file.bmp = file.gif = file.png]
Here is the Javascript to do it:
<script type="text/javascript">
function openBox() {
popup=window.open('','%item-name% - Preview','height=480,width=640,resizable=yes,scrollable=yes');
var win = popup.document;
win.write('<html><head><title>%item-name% - Preview</title><style>body{margin:0px;padding:0px;background:#000;}</style></head>');
win.write('<body><a href="%item-url%" target="_blank"><img src="%item-url%" alt="%item-name% - Preview" width="640" border="0"></a><body></html>');
}
</script>
And now all you need is a link to open it:
<a style="cursor:pointer;" onclick="openBox();">Preview Image</a>
There is many other ways you could do this, but this is one of the less complex ways. Have fun. And please remember that this is going to be opening the full size image just squeezed into a smaller image to fit the window, you will have to create a directory of preview images and re-route the url in the code to have a better effect.