7zip, is an extremely good freeware unziping utility. The reason it's needed for the audiogames archive, is that the files there are compressed using the 7z format which is unique to 7zip, and compresses to a much smaller size than your standard zip or ra files, hence why it's been used on the audiogames archive to save space.
I know the free version of winzip won't handle 7z format stuff, I'm not sure about the fully licensed one, but you can easily get 7zip from http://www.7-zip.org/
To unzip, just find the file in windows explorer and use the context menu to find 7zip and it's various extraction options.
Hth.
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)