Do you mean a regular Minecraft guide or Minecraft Classic? It would seem fun to play Classic on a PowerPC Mac. The game I would like to see compiled for PowerPC is Assault Cube. This last update they did killed PowerPC compatibility because their Mac coder got rid of his PowerPC Mac. My brother was so close to compiling it but it ended up giving him cryptic errors... I wonder if there are any PowerPC programming geniuses here who can compile the latest version of Assault Cube for PowerPC. I can contact my brother and tell him to send what he has so far.
If AssaultCube still supports 10.5 for Intel then it may be a relatively simple fix. If not then it will require quite a bit of recoding.