Try copying in the pertinent folder info for dccache, installed worlds, and library to see if your game will recognize them first, ZG. You might get lucky. I am pretty sure the download files won't work, but maybe the cache files will. It seems I was already to reinstall on my new system where I had to replace a couple discs (stuck in the CD player and borrowed, by not returned, by a friend). But, I got lucky, I think and I got some stuff to copy over. The saves wouldn't play, but the .nhd file from the saves would. So, I only had to open up and save in a world. Then, I'd quit and copy in the old .nhd file.
Steam version might not recognize the other formats, but it might.