   drag from outside into a SDL window
  if I drag and drop an item from outside a SDL window inside it , can I make SDL intercept that ?   
  Probably, if you don't mind doing it in a platform specific way.Look at SDL_SysWMEvent, for how to capture Win32 messages (assuming a Windows operating system). Then just figure out how to hammer it out using Win32. Beyond that, I can't be of much help, having never done it before.   