[angvelem]

Смотри в сторону хуков:

Код:

function MouseHook(Code, wParam, lParam: Integer): Integer; export; stdcall;
begin
  Result := 0;

  Msg := PMouseHookStruct(lParam);
  if (Code >= 0) and ... then
  begin
    // что-то делаем
  end
  else
    Result := CallNextHookEx(hMouseHook, Code, wParam, lParam);
end;
...
  SetWindowsHookEx(WH_MOUSE, MouseHook, 0, GetCurrentThreadID);