I had to change the shape of the sub in order for the collision for the walls to work properly.

As you can see, it's more like the Atari 2600 version, yet still has a little more detail to it. (Note the rings around the windows.) The title screen has stayed the same, though. I don't know whether to change it too, or just keep it the way it is. Anyway, you can find the latest ROM, source code, and all that other good stuff here. Feedback would be appreciated.