Thanks to a news tip from Alison, Dark Horizons has posted up as part of their July 24, 2003 update the possible movie release dates for Harry Potter and the Goblet of Fire and Harry Potter and the Order of the Phoenix:
Harry Potter 4 & 5: A November 2005 and June 2007 release are planned for the next two films.
I cannot help but emphasize on the planned part of that statement because like many plans, they are likely to change. Additionally this was in the films & rumours section. However, at least we have some sort of estimate.