Minecraft: Pi Edition is available for download
mojang.com
mojang.com
Also, here's a guide someone wrote up on using the prerelease pi.minecraft API, which might help you get started: http://www.stuffaboutcode.com/2013/01/raspberry-pi-minecraft...
Why won't they just do that with the real game??!
Last I heard, they were working with the bukkit team to produce an official api for the jvm version.
Here's the best part. On my (slightly tweaked) 512MB Raspberry pi, this runs flawless at fullscreen, way smoother than on my MacBook Pro.
The downside is that (in at least the early version I downloaded) there are no baddies, and nothing significant to mine.
I have a Raspberry Pi and I may look into Minecraft Pi to see how it looks as way to get young kids started with "programming". For kids who are already into Minecraft it looks like the Python API is a good way to get their feet wet.