Acting Auditions has some Eclipse casting info:
Summit Entertainment has started pre-production and casting for the sequel to Twilight, New Moon, based on Stephenie Meyer’s second book in the series, and to contain costs, the studio MAY be filming the third book, Eclipse, back to back using the same new director (this has not been confirmed). On Sunday, December 7th, Summit Entertainment did confirm that Catherine Hardwicke will not direct the films New Moon and Eclipse, and Chris Weitz has signed to replace her. Filming begins on New Moon in March 2009.
See it here!