Newsround has a great report up with lots of tidbits about the third, fourth and fifth movies - check it out!
Dawn French is in the new film
British actress Julie Christie [click for pictures] will play Three Broomsticks barmaid Madam Rosmerta. And comedienne Dawn French [click for pictures], last seen in the Comic Relief Potter spoof, will now play the Fat Lady. Professor Trelawney will be in the film, but hasn't been cast yet. But they're still not sure if Cho Chang will appear or not.
And:
"We will start pre-production [on the fourth movie] towards the end of the year, and start sometime next year. And [it'll] come out a year, year and a half after the third film." ... "My hope would be that it'll be the same cast, it's too early to tell though." is Heyman's comment. "We've only just started writing the screenplay. It's early days yet." ... There have also been rumours that Chris Columbus who directed the first two films, but isn't directing the third, will return to direct the fourth. "Maybe Film Five," says Columbus. "Four is starting a little too quickly, but Five is a possibility.