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

function GetText(Wnd: HWND): string;
 var
    textlength: Integer;
   Text: PChar;
 begin
   textlength := SendMessage(Wnd, WM_GETTEXTLENGTH, 0, 0);
   if textlength = 0 then Result := ''
   else
   begin
     GetMem(Text, textlength + 1);
     SendMessage(Wnd, WM_GETTEXT, textlength + 1, Integer(Text));
     Result := Text;
     FreeMem(Text);
   end;
 end;

 function EnumWindowsProc(Wnd: HWND; lParam: lParam): BOOL; stdcall;
 begin
   Result := True;
   if (IsWindowVisible(Wnd) or IsIconic(wnd)) and
     ((GetWindowLong(Wnd, GWL_HWNDPARENT) = 0) or
     (GetWindowLong(Wnd, GWL_HWNDPARENT) = GetDesktopWindow)) and
     (GetWindowLong(Wnd, GWL_EXSTYLE) and WS_EX_TOOLWINDOW = 0) then
     Form1.Listbox1.Items.Add('Handle: ' + IntToStr(Wnd) + ',Text:  ' + GetText(Wnd));
 end;


 procedure TForm1.Button1Click(Sender: TObject);
 var
   Param: Longint;
 begin
   EnumWindows(@EnumWindowsProc, Param);
 end;