When TeX and Ghostscript are in the right place, you finish the installation by unpacking the PP3 ZIP file and copying its content in the proper directories:
pp3.exe to an arbitrary directory that is in your
PATH.
PP3DATA to this directory.
For the sake of simplicity, I recommend to copy everything to
C:\Programs\pp3 and to set your PATH environment variable
to
old PATH;C:\Programs\pp3
and to set the PP3DATA environment variable to
C:\Programs\pp3. That's it.