The volcano tile set will replace your winter tile set. The mountains will be replaced by volcanoes (duh), and the earth will look like solidified lava. There are no changes in the gameplay (no new AIs).
To install it, simply run the exe file in your War2 directory and answer all questions with "yes". If you have problems, use a fresh maindat.war file (copy it from the CD to your War2 directory).
This tileset has been made by Chris fuller.
To get your old tileset back, either copy maindat.war from the CD into the war2\data directory or make a backup of that file first.