I'm using lights from some of the default texture packs that come with nexuiz. I insert the lights, some are dull, some glow but none trow off any light into the map. Why?

It would be useful to post which specific textures you mean.

Anyway, most light textures use a glow map (texturename_glow.tga), but not all of them also use a script that makes them emit actual light.

In that case, you need to put in light entities into your map yourself. You also can use "target_position" entities to give the light entities a direction (i.e. converting them to spotlights).