How to capture a window?

Hi

I want to make an application which will be able to capture any window I want.

For example: the application give me a list of windows which are on task bar. I choose one and my application creat a window in which will be captured window which I chose.
Not only screenshot but everything what will be done in chosen window will show in my applications window. Something like streaming from another window.

I know that maybe its not possible to do that only by qt so I will be pleased if anybody can give me reason for Windows.
If is possible in combination with qt becouse I want to stream this capture by QTcpSocket or QUdpSocket.

Thanks.

PS: sorry about my english...

May be you will have to write your own algorithm for streaming...
By the way mirror example in the link may help you :)

Thanks you but its not what I want. I need some reason for Windiows.
Have you any idea how to make that algorithm for streaming?