I would suggest you create a new library within poser. First create a folder called whatever you like, but Additional content might be a good idea. This is best in public documents but can go anywhere that poser can write to.

In this folder create a new folder called runtime.

Now in poser in the library panel is an icon that looks like books standing on end, with a plus symbol. Click on this and a window will open, navigate to this to the new folderyou have created and select it and click ok. This will now add a new library to poser and you can put you new stuff in it by merging the runtme folders from the zip files with the runtime you created, with no fear of overwriting anything already installed in poser