c# capture transparent window (Aero)

I need to capture an aero window and and make the window transparent there are several applications that do this so I know it is possible. I notice on every one of the applications that is display black then white under the window and then the capture happens. I think it is possible that they capture it on the black window to get the forms transparent color and then they capture it on white and then then somehow they set the transparent color and and up with the areo window that is transparent. I need some ideas that will work to accomplish this.