That might depend on your definition of nerd. I have heard different ones.
For me, a nerd is generally socially inept and it focused on one of a number of areas. Math, Science, Literature, Computers etc.
Geeks were always fans of a particular subset. So comics, Star Trek, Trains.
Nerds were awkward everywhere and often loners, geeks were awkward outside of their common interest groups.
Lately geek has become mainstream and can be attached to any subset. Glee, Harry Potter, Twilight as well as their traditional subsets.