@ aproctor: The advice is very good, however that was not the question the OP was proposing.  By the intent of the query, the OP wants to place an .obj file in an appropriate folder for access.  It sounds to me that the OP has just a mesh in .obj format. 

Unfortunately, there is no further information about it's relationship to Poser or whether there is a .cr2 file associated with it.  Giving more in terms of a solution, at this point, may prove confusing.