One method is to create a new folder within "My Documents". You can name it anything you like, suggest "My V4 Stuff". Within it create a new text file. Rename that file "Poser.exe"

Now run the installer, installing to My DocumentsMy V4 Stuff. The installer will be happy because it will see the (dummy) poser.exe file.

Then in Poser add My V4 Stuff to your library as per the Poser manual chapter 7.

Hope that helps.