My hat is off to the developer who sweated over this work and put it out there for free. You'll need to be at least a php hacker to get it integrated into your website, though it's not bad at only changing 1 file. And you'll also need to study how NGG Gallery works. And you'll need to websearch for helpful support given by the developer to other wordpress installers. If he didn't do that, this plugin would be a disaster because it's too hard to get working with what's in the FAQ, which is outdated.
It'd be nice if all those support questions were used to generate a new FAQ but that takes work and you haven't paid the developer a cent yet for his labor. :-)
So you'll need to work a bit to get it working, and if you do, paypal the guy something. At least enough to buy a beer for pete's sake!