Attached Link: http://lcrepiliere.free.fr/

Compose your scene as you would like your library thumbnail to look. Now render to a new window 91x91 pixels in size. Save with the same name but as a PGN file to the directory where your MAT file is stored. If you are using Poser 3 or Poser 4 you'll then need to convert this PNG file to an RSR using P3dO Explorer. (Link above)