Law is a tool (Score 1)

It's worth noting that civil lawsuits like this rarely happen unless someone a) considers someone a threat, or b) thinks they can make a lot more money than the necessary litigation will cost. If you don't make money off of it, or if the old material isn't making money anymore, it's unlikely that you're going to attract their attention.

Another thing: your intent matters. If someone does sue you, and they can show that you willfully intended to make a "clone" of their product, they have a much stronger case. Hell, this Slashdot story could very well be used against you as evidence. :-P So if you are worried about that, I would avoid making reference to the original work in whatever materials (i.e. websites) you release along with the game.