i've tried this in three different versions of Blender (2.57 with Yafaray & Lux, 2.58 with Yafaray & Lux, and plain, out of the box 2.58).  none have worked for exporting with this plug-in (for me).  that is, there are absolutely no options for the exporting tools.  there's a heading Poser Tools, but nothing underneath it. i haven't tried importing yet.

i've tried following your instructions pretty exactly in an effort to make them appear, but nothing has worked so far.  the only discrepancy i can find is that you say to put the plugin under Blender > Scripts > Addons, and every version i have has Blender, then a folder with the version number, then Scripts > Addons.  but other than that, i'm stumped.  i just downloaded the most recent version an installed it just to make sure the problem persisted before asking about it. 

if you have any ideas about how to get this working, i'd be very interested.  this obviously works for you, and the way this doesn't work for me is so absolute that i'm sure there's a particular cause.   and i'm aware it might be very specific to my setup some how, because i haven't seen anyone else mention the problem.   i'm just totally in the dark about what the problem is.