Go here...
http://www.7-zip.org/
Download the .exe version 4.42 and install it. This will allow you to decompress the 7z file.
As for JSGME...between jones' web site and the readme file it should be self explaining...and actually quite easy to use. If you still don't understand it, email Jonesy, he's a pretty good guy and im sure will help you sort it out.