CDV has it scheduled for release by Q1 2002, or "real soon now".

After the worldwide hit Cossacks: European Wars comes the expanded Cossacks: The Art of War. The focus is on an improved and more dynamic single player mode with adjustable difficulty. In addition to that the internet play and community features were greatly improved allowing players to check out each others histories and review recorded games.
New units, nations, ships, a map editor, joining forces with the computer and exchanging resources all together take Cossacks to a new level.

Official "Cossacks: The Art of War" website