Your BS detector should be bleeping at full force. There is a long, long history of failed attempts to build ducted wind turbines. The fundamental question is whether, for the revenue you'll gain from the energy gains, it's more efficient to put the money into building a duct or extending your turbine blades a bit more. Unfortunately, building all the extra structure to support the duct is expensive.

The history is long and discouraging. Paul Gipe has some good photos of recent attempts: http://www.wind-works.org/cms/index.php?id=541