Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

function IsWindowTopMost(hWindow: HWND): Boolean;
 begin
   Result := (GetWindowLong(hWindow, GWL_EXSTYLE) and WS_EX_TOPMOST) <> 0
 end;

 procedure TForm1.Button1Click(Sender: TObject);
 begin
   if isWindowTopMost(FindWindow('notepad', nil)) then
     Label1.Caption := 'Window ist topmost'
   else
     Label1.Caption := 'Window ist not topmost';
 end;