How do I bring an unmanaged application window to front, and make it the active window for (simulated) user input

If you don't have a handle to the window, use this before :

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

Now assuming you have a handle to the application window :

[DllImport("user32.dll", SetLastError = true)]
static extern bool SetForegroundWindow(IntPtr hWnd);

This will make the taskbar flash if another window has keyboard focus.

If you want to force the window to come to the front, use ForceForegroundWindow (sample implementation).

This has proved to be extremely reliable. The ShowWindowAsync function is specifically designed for windows created by a different thread. The SW_SHOWDEFAULT makes sure the window is restored prior to showing, then activating.

    [DllImport("user32.dll", SetLastError = true)]
    internal static extern bool ShowWindowAsync(IntPtr windowHandle, int nCmdShow);

    [DllImport("user32.dll", SetLastError = true)]
    internal static extern bool SetForegroundWindow(IntPtr windowHandle);

Then making the calls:

ShowWindowAsync(windowHandle, SW_SHOWDEFAULT);
ShowWindowAsync(windowHandle, SW_SHOW);
SetForegroundWindow(windowHandle);

    [DllImport("user32.dll")]
    public static extern bool ShowWindowAsync(HandleRef hWnd, int nCmdShow);
    [DllImport("user32.dll")]
    public static extern bool SetForegroundWindow(IntPtr WindowHandle);
    public const int SW_RESTORE = 9;

ShowWindowAsync method is used to show the minimized application and SetForegroundWindow method is used to bring on front the back application.

you can use these methods as i used in my application to bring the skype infront of my application. on button click

private void FocusSkype()
    {
        Process[] objProcesses = System.Diagnostics.Process.GetProcessesByName("skype");
        if (objProcesses.Length > 0)
        {
            IntPtr hWnd = IntPtr.Zero;
            hWnd = objProcesses[0].MainWindowHandle;
            ShowWindowAsync(new HandleRef(null,hWnd), SW_RESTORE);
             SetForegroundWindow(objProcesses[0].MainWindowHandle);
        }
    }