I select all files and unzip them into one folder, which I keep separate on my external HD. The rest is handled like you wrote. I copy all the unzipped content into the Public/Public Documents/Poser Content Folder. Don't copy the stuff into the runtime folder, that would be a mess.
Next thing is to start Poser and refresh the library. The content should be ready to use now.
Hope that helped, have fun and happy rendering.