this addon for blender is a slimmed down version of Campbell Barton's ,wavefront obj exporter,
rather it borrows the important parts,
instead of a mtl file it exports a proper obj.cfg file along with the .obj
as long as your textures are in the same folder as the exported .obj/obj.cfg everything should work in one step.

make sure the objects you wish to export are selected, other than that install use like any other addon.
have fun,
angjminer