I had a slightly different problem (wanted to link each image to its own page) so I’m not sure if this will help, but the place to find the link is in nggSmoothSharedFunctions.php.
This line is the link:
$aux["link"] = BASE_URL . "/" . $picture->path ."/" . $picture->filename;
If you only have one smooth gallery and you want every image to link to the same place you can hard code the URL to your gallery. eg change the above line to:
$aux["link"] = BASE_URL . "/gallery";
Otherwise you can use the gallery id in the link to distinguish between galleries: $picture->gid;
The options for opening in the new window and hover text are in this line at the bottom of that file:
$out .= " <a target=\"_blank\" href=\"" . $picture["link"] . "\" title=\"View project info\" class=\"open\"></a>";
I know there is probably a better way to do this, but I hope it helps.
