Walk-through: Import the object and add appropriate textures.  Make sure the object is selected, then go to the Props library.  Click on the plus sign to add to the library.  Give it a name, and click OK.

If the prop has multiple objects, each should be parented to the main part or another part that is parented to the main part (Properties - Set Parent).  Select the main part to add to library as before.  After giving it a name, click on Select Subset button.  In the dialog that comes up select all parts of the prop, then click OK.  Click OK on original box to add to library.

If you had to resize or move the object before saving, you can still have it with all the parameters zeroed.  Export the object to OBJ, then delete the original object.  Import the one you just exported, UNchecking all the options on import.  It will load exactly where the original was, but with all dials zeroed.  If multi-part, each must be exported and imported separately to keep Poser from making it all one object.  Reassign parenting and save to library.  I hope this helps.

John