Well, a lot more has changed since yesterday. I put in jumping, and opened the castle up. Inside the castle, the same music from the N64 version plays, only it's very simplified down to meet the 2600. None of the doors work yet. Well, you can read more and download the binary here: http://www.atari2600land.com/sm642600/
I also figured out how to make it so player 1 (Mario) can go in front of player 0 (door), I remembered a topic addressing this in the bB forums and sure enough it was still there, so I downloaded the appropriate files. My eye hurt last night while I was working on this, but it's much better now (the eye as well as the game.) Next up, opening the first door. I don't know how I'm going to do this, though, since the doors move left and right. I'm planning on doing something with this which is why I programmed it in. Maybe a fourth door to the extreme right or something.