Most Poser content will consist of three main components: a Poser file, a geometry or mesh file, and one or more texture map files. Each of these has a specific location within the Poser Runtime folder into which they will be placed in order for Poser to recognize them. The Runtime contains all of Poser's libraries, and installing new figures, props and poses requires that one become at least somewhat familiar with its structure.
The Poser files are the library files that the application uses to load figures, props, poses, lights, etc. These files have extenstions such as .cr2 (figures), .hr2 (hair), .pp2 (props), .pz2 (pose), .lt2 (lights) etc. Poser Pro Pack, 5 and 6 also support binary compressed versions of these types and the extensions will change slightly replacing the '2' or '3' with a 'z' to indicate that they are zipped (e.g. pzz, crz, p2z.) These files need to be placed in the appropriate library directory found within the Poser Runtime folder, (e.g. Poser/Runtime/libraries/Posermflap.pz2).
Earlier versions of Poser (prior to Pro Pack) utilize a .rsr file to store the preview picture that appears in the Library palette. The .rsr needs to accompany its equivalently named Poser file in the directory. If using Pro Pack or later, the preview is in the form of a cross-platform .png file, however this can be treated like a .rsr file. It should be placed in the library directory along with its similarly named Poser file.
Mac® users may need to use the Classic Maconverter utility from Softrabbit to convert the rsr files back into image resources that the OS X version of Poser can display. PNG files as noted are cross-platform.
Another component of Poser content is the geometry or mesh data file which will have an .obj extension. This file will need to be stored in the Geometries directory within the Runtime. Determining the correct location for the .obj file is a bit tricky since the Poser file (CR2, etc.) will determine the exact path required. You can find the required location by opening the Poser file in a text editor (compressed Poser files can be decompressed by most utilities that can open ZIP files.) Look for the the string "objFileGeom" or "figureResFile" and look at the subsequent path. This will describe where the .obj needs to go inside Geometries. It is likely that, if you have been given the content or downloaded it, the .obj is already in a directory that can be placed into the Geometries directory in the Runtime folder. Look at the folder structure that the decompressed content provides; this tells you where the various files should go within your Runtime folder.
The last component of most Poser content is the texture map(s). This will usually be one or more image files in the format .jpg, .psd, or .tif. Similar to the mesh files, the textures will go in the Textures directory within the Runtime folder but will likely reside in a subdirectory as specified by the Poser file. Again, you can open the Poser file in a text editor and search for "textureMap" and look at the following path.
Typically, content is provided in a zipped format that maintains a pared-down mini version of the Poser Runtime. When unzippe,d the content files will be in their required directories in this Runtime clone. Windows® users may simply drag this Runtime directory to the Poser directory and allow Windows to place the files where they belong (or copy the mini-Runtime and paste it into the Poser 6 folder; when Windows alerts you that there's already a Runtime folder present, click the Yes to All button, and Windows does the rest.) Mac users will need to drag files and folders by hand from the mini-Runtime into the corresponding locations within the Poser Runtime.
Note: Poser Pro and Poser versions later than 6.0 use the PMD file format, to store external binary morph information. PMD files should be placed into the same directory as the CR2/CRZ files that they supplement. These files are not compatible with earlier versions of Poser, and figures that use PMD files will not display all of their available morphs in other applications.