There was a rumor in the newspapers of UK about "Harry Potter and the Deathly Hallows" in which they stated that the movie will be split in two so the original author (JK Rowling) intentions remained complete for the movie. It is unlikely this information is true, because no screenplay or storyboard (by Steave Kloves) has been developed and won't be until the writers' strike end. There has not been any official declaration from WB (updated, February 09, 2008).
EDIT: IMDB Had an article about how it was confirmed but the actors are only contracted to seven films so they mightn't risk it