You really don't need to create the empty sub-folder structure. Just create a new folder and name it for your new runtime. Install products there and the sub-folders will be created as necessary. Poser5 doesn't seem to care whether the folders are there or not. Once you have your new folder created you must link to it from within P5. You do that on the library tab by navigating to the top of a library where you can see the "Poser 5" and "Download" runtimes already there (you can't delete those) - then at the bottom of that library use the "+" symbol to add your new folder to the list.