I also second the recommendation for the book The Mislabeled Child by the Eides. The book distinguishes between many different types of issues that are sometimes confused with one another. ADD is one of the topics.

Also, there's a recent thread on one of these boards on ADHD and giftedness, which I haven't read through yet.

And an interesting link I came across once upon a time http://borntoexplore.org/gifted.htm about how difficult it may be to distinguish between giftedness and add/adhd - more food for thought.