I would suggest the best way to organise the content in the way you want is to create new runtimes and add these to poser. Somewhere on your drive that poser can write to create a folder named whatever you want ( a descriptive name of the sort of stuff you are going to put in this runtime) and in this folder create a folder called runtime. Now in poser you add this runtime to your content by clicking on the symbol of upright books with the plus near the top right of your library window. This opens a window that allows you to navigate to the folder you have created, select this and poser will add a runtime to your library.

Now if the content is correctly structured within the zip folder you can use the install from zip archive to add content to this runtime.. (If the zip file doesn't have runtime folder as one of its top folders you have to install manually)