Hello KK255,
There is a great overview located here about ADD vs ADHD. Some of the sections include an article about the subtle differences by Eileen Bailey, a resident expert here. There is also a good article here about differentiating between the two and the different treatments for each.
You might also be interested to know that there are related conditions that can mask a diagnosis of one or the other. You can read about those here.
I hope you find this useful. Please stay in touch and let us know how you are doing!Vicki M