Want to buy a small wind turbine of sizw 400W out put.
Where will I get it? what is the Cost? How much is the weight of the system?

Southwest Windpower has a 400 Watt turbine on the market called the Air X. It comes in two models: the Air X and the Air X Marine. Here is Southwest Windpower's website so that you can learn more about the machine and find a dealer in your area:

www.windpower.com

Before you buy a small wind turbine I would suggest that you do some homework by reading the Small Wind Electric Systems Consumers Guide located at the link below. It will give you some good background about what is involved in a small wind system installation:

http://www.nrel.gov/docs/fy05osti/37633.pdf

I hope this helps and please feel free to post again or call if you have more questions or concerns.