First decide on the names of the runtimes you want. It is easiest to do this at the beginning rather than try to re-organise later. It is easy to add more runtimes later, and possible to merge runtimes, but if you want to split runtimes that basically entails re-installing your content, so best avoided.

In somewhere like public documents (somewhere that poser has write access to) create folders with the names of the runtimes you want, and in each of these create a folder called runtime. . Now you can add these runtimes to poser. In the library panel is an icon looking likes books with a plus symbol. Clicking on this opens an explorer window, navigate to one of your runtimes and click ok, this will and the runtime to your libraries. Repeat until you have added them all.

To add your content to these, check the zip file to see if the first folder in it is called runtime. If so you can use the install from zip archive in the poser file menu. This will open a drop down menu from which you can choose the runtime into which you wish to install it. Otherwise you need to unzip the file and move the runtime folder into the library name folder you have created so it merges with the runtime folder already there.

Once the content is installed you can move it around inside the library to better organise it if you wish. I find this easiest to do in explorer rather than in poser itself.