[Plugin: NextGEN Gallery] Adding more effects

I’m having trouble adding more effects to NextGen. I’m not sure where to put lightbox, slimbox, highslide, etc. directories, but wherever I put them, my effect doesn’t work. The only one working is thickbox (the one that comes preinstalled).
I noticed the thickbox is a directory in the nextgen directory (plugins/nextgen-gallery/thickbox), but installation instructions often tell me to put the effect directory in the plugins directory (plugins/lightbox etc etc). Also, when I download an effect library, it is usually called highslide-4.0.1, with another directory inside that called highslide. Which is the directory I should be copying over, and again where should it go, the plugins directory or the plugins/nxtgen-gallery directory?
Thanks for any help.