[Darvin]

I've only heard of modders getting into copyright issues a couple times, and it's usually when they're doing something like making a starcraft mod for command and conquer (that really happened and Blizzard issued a C&D). Unless you're making a blatant ripoff of another existing game in your mod, you shouldn't run into problems. As for mappers, never heard of them running into legal trouble, don't worry about it.