If it's a hack of a ROM, you need an emulator to play it. You may need the ROM file as well, as most hackers only release a patch for their hack and it's up to you to find the illegal game files. As for which emulator, that would depend, in part, on which version of Duck Hunt was hacked. If it's the NES version, then you have a couple of hundred or so emulators to choose from. I'm quite fond of Nesticle, but Nestopia or FCEUX might work better for you, depending on your setup.
