If the Obp files are already in Bryce libraries then just copy those libraries into the preset folders (but obviously under a different name so you don't over write anything) 
Once you have gone in and made sure the preset libraries are set up correctly by making sure there is no additional folder in the area you shouldn't have any problems. the object presets should be in presets/objects and not presets/objects/objects.  Until they are set up correctly Bryce will refuse to let you add anything through the create area