I just finished my HACK computer in Minecraft as well. Two weeks ago I didn't know much about CPU's at all, now I can build one thanks to this site :) Here is the forum thread that has all my process of building it, video, save file, diagrams and any future updates.
http://www.minecraftforum.net/topic/526445-my-alucpucomputer-progress-thread-video-and-worldsave/I added bi-directional bit-shifting, XOR and RNG functions to the ALU, by using the 2 free bits and a small decoder. I also reordered the instruction-set a little for minecraft specific reasons. Other than that it is the same CPU as described here.
This has been a great resource, thanks!