Looks to me that AdventureRunningSystem is basically a "make your own game" kind of developement set, which used cwave format in earlier versions (but now uses Ogg Vorbis instead). Likely is that your game was made with this thing.
The latest version (dating 2004) of the SDK that you linked does not include the cwave tools so you'll need to find an older version.
The SDK itself is downloadable from
http://www.vector.co.jp/soft/dl/win9.../se235667.html, but they blocked web.archive.org so you cant download older versions with that.
edit: the latest version of said SDK is up at
http://buin2gou.com/advrun/. buin2gou.com is the homepage of the author of this developement set.
edit2: looking at the changelog of the SDK, it seems that the cwave tools were replaced with Ogg Vorbis at 2002.12.03. Your best bet at decoding these files is finding a version of this SDK that dates before that.
edit3: And that ain't gonna happen. archive.org has no copies of older versions of this SDK, and absolutely no sites hold any reference to it, other then the one you posted (and that one direct links to the vector.co.jp download service, so the link would be broken even if the file was there). Your best bet would be emailing the author of the SDK and hope that he understands english and still has a copy of the cwave tools.
Jam it back in, in the dark.