A
MSDN:
Visibility of Taskbar Buttons
The shell creates a button on the taskbar whenever an application creates a window that isn't owned. To ensure that the window button is placed on the taskbar, create an unowned window with the WS_EX_APPWINDOW extended style. To prevent the window button from being placed on the taskbar, create the unowned window with the WS_EX_TOOLWINDOW extended style. As an alternative, you can create a hidden window and make this hidden window the owner of your visible window.
The window button typically contains the application icon and title. However, if the application does not contain a system menu, the window button is created without the icon.
If you want your application to display a message to the user while its window is not active, use theFlashWindow function to let the user know that a message is waiting. This function flashes the window button. Once the user clicks the window button to activate the window, your application can display the message.
