Just in from /Film [1], which is citing Variety [2]:

Warner Bros has announced that McG’s Terminator Salvation: The Future Begins will hit theaters on May 22nd 2009. This means that Terminator 4, which begins production in New Mexico for two months on May 5th, will go head to head with Fox’s Ben Stiller family comedy sequel Night at the Museum II: Escape From the Smithsonian.

Click here to read the full /Film report! [3]