The .OBZ file is a compressed .OBJ file.  You will need to uncompress it.

You can find the uncompress/compress option in the window tool bar of Poser when you have it open.  

Window / Python Scripts / Utility Function

This is the "Compress" option.

You can choose to compress object files in Poser 6 and Poser 7.  That option is not available in Poser 5 however.  I find that .obj files can take up much space, so I always compress those now.

You can also choose to keep or delete the original uncompressed files.  Personally I see no reason to compress a file to save space, yet keep the original uncompressed version too.  So I always check to delete the original uncompressed file.

You have the same options for "uncompress" too.

Again, when you are asked to browse to the folder you want to compress/uncompress, while I'm showing a Runtime folder, you can pick any single folder inside, you do not have to do the whole folder if you do not want to. For example, sometimes I will need to uncompress a single .obj file. What I do is browse to the Geometries folder and locate the folder that contains the .obj file I want to uncompress or compress, and just work on that folder.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi