pp2 (poser prop) goes into a folder inside the Poser/Runtime/Libraries/Props/[foldername] If they're 3ds, dxf, obj or any other kind of format other than pp2 (ppz for Pro Pack compressed) they need to be imported into poser through the File Import menu and then added to the props library by the little add (+)sign. It would help a little bit to know what sort of files you've downloaded that you're having trouble with. Another possible problem might be that you are extracting to the props/[folder] directory with Winzip and have "use folder names" checked, which means the props are several layers deeper than they should be and Poser can't see them. Hopefully that's of some help.