Well, the new movies, (Evangelion 1 and 2.0), are a retelling of the original story, but death and rebirth, and the end of Evangelion, are to be watched at the end of the original 26 episode series.
So, you can either start with the two new movies, or watch the original series, then death/rebirth and the end of Evangelion, (death and rebirth really isn't necessary since it's mostly recap), and then check out the new movies.
Hope this helps. :)