Dockable Windows...How??

I've got an app in the planning stages in which I would like to use a dockable window. This window will contain a treeview to display a small file structure. How do windows programs accomplish this feat?

Thanks,
Phil

From looking at the MFC source code, I figured that they implement their own method. It seems that there is no built-in way. You'll need to get the right messages (WM_MOUSEMOVE or WM_MOVE or such) and handle them in a way to check where the window is and set it's pos to the frame of the parent window if near enough. You'll need to implement your own way to do that.