Judgeing by the way Poser 4 installs over Poser3... you can decide whether to over-install or make a new installation. It has been stated that P5 will be fully backwards compatible indicating to me that the library structures will be the same, but with additional folders. All addidional content will just be added to your libraries on install. The P5 installer won't delete stuff which is already there. The chaps and chapesses of CL will have thought this through to make upgrading as painless as possible. The only difference that I can see within the libraries is the ability of the folder tab to navigate deeper into any folder structure within the folders. You'll probably have to move files into sub-folders manually... but they show up as little folder symbols in the library panel. H:)