(Original message edited)
I just added the Lightbox Extension to my blog site, which run with BlogEngine.NET.
All you have to do, is to implement the lightbox (see: http://blog.data-worx.de/page/Extension-Lightbox.aspx) and make you hyperlinks like this:
title="Nice wild horse, close-up (Summer 2007)">
alt="" height="100" />
(with thanks to René Kuss)