Here's text from the Poser 8 README.rtf  that may provide a place to start:

"Content Library Search
  - When filtering content categories, Poser returns search results that contain individual items with matching name and type as well as folders with names that match the search term, regardless of whether or not they contain items of the filter type.
  - For best results, please ensure that Windows Search 4 is installed (Windows only). Search 4 is installed by Vista SP2, the stand alone installer is available for other supported operating systems at http://support.microsoft.com/default.aspx/kb/940157
  - Poser enables indexing for all content library runtimes that are added to Poser (Windows only, enabled by default on Mac OS X).
  - Indexed search does not cover network volumes (Windows only). There is a possibility that a patch from Microsoft would enable that (http://support.microsoft.com/kb/918996), but we haven't verified that and therefore don't recommend installing it."

Steve Cooper
Poser Product Manager