Once they are placed in the correct folders they should show up in Poser. I suggest looking into the folders the items are suppose to be in to make sure they are showing up there. If not, I suggest trying the following:
Make sure the product was actually for Poser. If so, contact the freestuff creator to ask for a suggestion why the product is not working. If you do not get an answer from the creator, please email email@example.com. We can look into it for you.