Following today's standards Poser no longer looks in the program files folder for content. 

To my recollection: make a folder in which you want to store your V4 stuff and add a file named poser.exe and asubfolder called Runtime. That Poser.exe can be an empty file. It just serves to fool the installer.

Add that folder to your library. This will make Poser add the substructure.

Then run your V4 installers there. This should give you an independent working installation that you can henceforth copy and move around as you wish, address from any Poser version, etc. Delete the poser.exe dummy to avoid future confusion .