Over the past couple of days I've been trying to re-implement the server protocol from Minecraft Beta 1.1_02. I started off trying to do the last version of Alpha, 1.2.6, but realized that multiplayer is kind of fundamentally broken in Alpha for lots of reasons. So instead of Alpha, I decided to go with beta. So far, I've just been able to "generate" a flat world and allow the player to properly authenticate, but there are a lot of packets to handle and they're not all obvious. Below are some screenshots.
Oh and there's a git repo too:
The instructions are the last resort.