According to the official website, "TRIGUN THE MOVIE
" will be premiered in the Spring of 2010. The cast of the main characters are the same as that of the TV series.
The story takes place in a desert town Macca. The Mayer Kepler collects pothunters to counterattack a legendary thief Gasbag. Meryl and Milly visit there to assess the insurance and are surprised to see Vash in the town. Finally the gangsters of Gasbag attack Macca and Vash find Wolfwood among them.
Source: Trigun The Movie official website