They're not zip files, but installers made with an application. As far as I can tell the installers are made with Install Maker from Clickteam, at least it looks a lot like it. These install applications use there own compression and protection format, which cannot be opened by any other application, only by running the execute file.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk