Of course, both words have many meanings and quirks (I hate when words can mean several things, don't you?). Simplistically, I think of argumentation as a sort of process where you put everything together in your head to present your points of view, or even put things in your head with things in other people's heads to arrive at a conclusion. The first would be the skill of ordering thoughts prior to a discussion, and the second would be the actual discussion. An argument brings with it (but not always - eg. lawyers' or politicians' arguments) the idea of tempers being lost.