Sure. There are many tools that can open up (uncompress) a gz file in Windows. For example, Total Commander (http://www.ghisler.com) is a nice shareware file manager for Windows that includes this ability.
There is no such thing as .scj. However, there is .scm that is used by by StarCraft as a game map. .scm includes various types of terrain and resources and are created in different sizes, including...