Sounds indeed a bit more tricky than with Apache2. But still relatively easy when compared to some other server configurations: try Postfix if you like headaches

Will lighttpd be enough for the IMCDb, all the more with the (most probably heavier) code of the NextGen? I use it on my computer for "internal" tools and for testing html/php pages and scripts, but feel more "comfortable" when having an Apache for online sites...