BBC News Online has the story (contains a spoiler about next week but it’s clearly marked at the end). In brief: the next two series will also be thirteen episodes, and there will be two Christmas specials made, giving a total of twenty-eight episodes which have yet to be made.
Additionally, Russell T. Davies has confirmed that Billie Piper will be in all of series two (contrary to previous reports). He will write six episodes of series two himself, and the series will see the return of the Cybermen.
Filming on series two is due to begin in five weeks’ time.