WS_EX_NOACTIVATE
Windows 2000/XP: A top-level window created with this style does not become the foreground window when the user clicks it. The system does not bring this window to the foreground when the user minimizes or closes the foreground window.
To activate the window, use the SetActiveWindow or SetForegroundWindow function.
The window does not appear on the taskbar by default. To force the window to appear on the taskbar, use the WS_EX_APPWINDOW style.