At times, it is necessary to get a handle (HWND) to the shell’s main window.
MSDN offers us next method:

hwndShell := FindWindow(‘Progman’, nil);

It seems to be a simple code but I’ve found much better solution.
The User32.dll has one more useful and of course
undocumented function – GetShellWindow!

// This example will show you how you can obtain a handle to the
// Windows Shell window without calling the FindWindow function.
// Translated from C to Delphi by Thomas Stutz
// Original Code:
// (c)1999 Ashot Oganesyan K, SmartLine, Inc
// mailto:ashot@aha.ru, http://www.protect-me.com, http://www.codepile.com

// This function returns a handle to the Windows Shell window

function ShellWindow: HWND;
type
  TGetShellWindow = function(): HWND; stdcall;
var
  hUser32: THandle;
  GetShellWindow: TGetShellWindow;
begin
  Result := 0;
  hUser32 := GetModuleHandle('user32.dll');
  if (hUser32 > 0) then
  begin
    @GetShellWindow := GetProcAddress(hUser32, 'GetShellWindow');
    if Assigned(GetShellWindow) then
    begin
      Result := GetShellWindow;
    end;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  hShellWindow: Hwnd;
  strWinText: array[0..260] of char;
begin
  hShellWindow := ShellWindow;
  if hShellWindow <> 0 then
  begin
    GetWindowText(ShellWindow, strWinText, 255);
    ShowMessage(strWinText);
  end;
end;