Unfortunately, there is no marathon after all But it looks like starting Sept. 28th, they will be showing 1 episode every week starting with the Pilot

09/28/2006 05:00 AM ROSWELL ROSWELL - PILOT
10/05/2006 05:00 AM ROSWELL THE MORNING AFTER
10/12/2006 05:00 AM ROSWELL MONSTERS
10/19/2006 05:00 AM ROSWELL LEAVING NORMAL
10/26/2006 05:00 AM ROSWELL MISSING (ROSWELL)

But check your local listings