I just set mine to my external runtimes folder, which contains ALL my runtimes ;)...hehe. So far, Luxrender has been able to find everything ;).

As for your glowing skin problem, most skin texture poses have ambience in them. It's always a good idea to double check the emitters panel and make sure none of your skin textures are going to be giving off light and set them to be ignored. You can also set all ambience in the entire scene to be ignored with the button. Only use that if you don't have any valid emitter light sources.

IMVHO, emitters give off a much more pleasing light with softer shadows than actual lights do. But that may just be personal preference ;). That excludes the sun of course.

Laurie