what is an mtl file and where should it go in poser, eg props,poses. and why do I get thumb nails of things but when I try to click them the poser box tells me they are there when there is nothing in the box showing?

mtl = material. When some apps create an obj they create an mtl to go with it. Once imported into Poser, you don't need the mtl any more. I think.

I don't understand the second question.

Yes, an file with an mtl extention is a file that carries the material information (e.g. texture/colour) for a file with the same name but with an obj extention. It must live in the same directory as its associated obj (Waveront Object)file. Poser does not care where obj files live UNLESS they are associated with(linked from)a pp2 or cr2 file. You need to keep the mtl file (unless you resave it as a pp2), otherwise the object won't display the correct materials. Poser 4 does not have a any set place to put obj files that are not associated with cr2 (character), or pp2 (prop) files. I create a sibdirectory under Poser 4 to put them in.