One of the first things I do when I install something is to delete all the P4 files. They are actually dangerous in Poser 5 and Poser 6 because a lot of them ask for missing .bum files and this can hang your system. Apparently Poser 4 had the ability to create .bum files, but they aren't needed in Poser 5 and Poser 6. PP files are safe to keep and can be used in Poser 5 and Poser 6.