I just wrote a travel article about this that will run in the National Catholic Register. A few points to add to Anna-Marie's info:
*The church’s 1211 consecration will be recreated through a solemn liturgy on Saturday, May 7, incorporating the cathedral’s 12 Crosses of the Consecration.
*The cathedral museum was redone in honor of this celebration, so check that out.
*The new City of Culture is opening -- it's a futuristic building in Santiago that has a bunch of components, like a historical section, theater space, etc.
*As Anna-Marie said, there are lots of exhibitions on the cathedral’s construction, and a wide variety of cathedral concerts.
The PR people for all of the celebrations wouldn't release any specifics until March 15 (even to journalists), so maybe there will be more info online once the 15th rolls around.
Melanie