I was able to open the zip folders to see the folders inside using StuffIt Expander. From there I just started moving the necessary data manually. Took a while, and not everything is working perfectly, but I'm getting there. I'm sure there are better ways of doing this and I'm probably still doing some things wrong, but as a great Captain once said, "We learn by doing." Thanks again for all the feedback.

Thank you for the feedback. However, I think I may not have been clear in my original post. I am running Poser on a Mac, so I'm not sure if the Windows solutions apply...? In addition, I cannot, for the life of me, open these folders (like one is called PoserPremiumContent_3DScenery_01.zip. If I double-click on that, it opens toPoserPremiumContent_3DScenery_01.zip.cpgz. If I then double-click on that, it opens PoserPremiumContent_3DScenery_01 2.zip, and it would just go 'round in circles, opening and re-creating the same 2 files. I never get to see what's actually living inside the folder! I'm truly baffled...