I also saw a commercial on Nick. It says that starting on July 14th (monday) at 8PM and ending July 18th (friday), there will be new episodes of Avatar (a total of 5 new episodes). And Saturday July 19th at 8pm, is the hour long finale, "Sozin's Comet". Check it out at www.nick.com/summer/
Doesn't it seem that Nick is trying to get rid of Avatar? Playing all the new episodes in one week. It's a little weird. But at least they are playing the new episodes!