Yeah, difference of agnostic and atheist is a really blurry line and most people are confused by it. Most people think atheist = believes god does not exist, which can be true for a specific atheist but is not necessarily true for all atheist. Atheism is actually quite a large category that can encompass many different things (including agnosticism).
This video should help people:
http://www.youtube.com/watch?v=sNDZb0KtJDk
There is so much confusion about the terms "atheism" and "God" that it makes it almost impossible to debate with one another. You need to have well defined definitions in order to make any sort of logical argument, and if people are using different definitions than one another it makes the argument worthless.