I've opted for judging this year, so I'm not entering. However, I can't resist playing about and not entering means I can bend the allowed rules a bit. So...
I've started trying to hack up the existing java gameboy emulator so it fits inside our beloved space limit. However, I'm not quite there yet. It's currently at about 6k compressed and pack200.gz. Since I haven't got the server side stuff for pack200 at the moment you'll need Java 1.6 to try out mario land 2:http://www.cokeandcode.com/applets/gameboy/mario/
I'll post the code if anyone feels like hacking at it some more to get it down some more.