Attached Link: http://www.renderosity.com/~pzr/extensions.html

As jchimim says, if you unzip the downloaded file, you will usually see which folders the files belongs in. At the link above, you will find a good overview of the different file types you will encounter in Poser and where they belong in the folder hierarchy. (The link is to a section in the "Poser Resources" page you will find if you click on the banner further up on this page)