I was specifically interested in displaying a small NextGen Photo Gallery in Excerpt section of a blog post. The solution was as simple as swapping out the_excerpt(); for echo do_shortcode(get_the_excerpt()); in the ‘category.php’ file.
For more in-depth info, I suggest you check out this post from Mummy.org
Thank goodness for Google, and for bloggers who use good keywords and phrases in their writing. And thank you to Mummy.org for sharing how to use NextGen Gallery code inside a wordpress excerpt.