The next version of NextGEN gallery contain a extended Slideshow support for the sidebar or header. This function is called :

function nggSlideshowWidget($galleryID,$Width,$Height);

So you are able to integrate a widget into your theme manually , or automatic via the widget function into your sidebar. If your theme didn’t support the sidebar widget use the follow code in your theme :

<?php
if (function_exists("nggSlideshowWidget"))
nggSlideshowWidget($galleryID,$Width,$Height);
?>

For random images :

<?php
if (function_exists("nggDisplayRandomImages"))
nggDisplayRandomImages($number_of_pic,$Width,$Height);
?>

For recent images :

<?php
if (function_exists("nggDisplayRecentImages"))
nggDisplayRecentImages($number_of_pic,$Width,$Height);
?>