The title announcement for the theatrical version Pocket Monster Diamond & Pearl will be announced in the January issue of CoroCoro Comics. The movie is scheduled to open in the summer of 2007 in Japanese theatres. The January issue of CoroCoro is scheduled to go on sale December 15. We should have the title sometime around that date.
The official site is currently running a weekly Movie 10 teaser with pictures from the post production of the movie. You can view them at http://www.pokemon-movie.jp/rokehan/index.html