There is an online version of this game which I LOVE! Pentago Online. It is a great tool for learning the game. Often, when kids begin to play, they forget to turn a piece of the board after they've placed a marble. The online game won't move on until the board is moved. Also, the online game allows players to play against a friend or against the computer. Playing against the computer is a great way to practice great strategies.
Plus, the sound that the online version of the game makes when someone wins makes the library a very happy place.