OK now I think I understand.
You can check my site and click a thumbnail, see if that's what you want.
If it is use the following :
Lately I've been recommending the following :
Now I use jQuery Lightbox (balupton edition).
Make sure in Gallery->Options->Effects had the following setting :
Link Code line: rel="lightbox[%GALLERY_NAME%]"
You'll see the download.
After the plugin has been installed you find jQuery Lightbox in the setting section of the admin bar.