When you open Poser and you have your library pallette open (the one down the side in a fetching shade of beige :o|) you will see a big + in a circle left click on this and a screen will pop up that allows you to navigate through your PC to add additional content.  You will, on a typical installation, navigate to C:/ProgramFiles/Curious Labs/Poser 5/Runtime left click on the Runtime folder under your Poser 5 installation and then hit okay.  You will now find that your main menu (keep clicking up on your libraries palette until you can go no further) now shows Poser 6, Downloads and Poser 5. This is your Poser 5 Runtime and you can access anything installed to that Runtime directly through Poser 6.