From gamesradar:

In a recent conversation with Gametrailers TV, Glen Schofield, General Manager of EA Redwood, revealed some juicy details not yet released to the public about the game. “Prequel takes place 3 weeks before Isaac gets to the Ishimura, Isaac is not even in the game but there is a couple people you will be playing with, but there is a woman you’ll need to save” he continues, “Flamethrower is back, have a different couple pistols, a coupel i cant talk about. You actually start off on the planet(which in the original they talk about but you never see), then go to the ship which is inhabited at this point so you get to see whats going on." Seems like this prequel is starting to take shape and we couldn’t be more excited.
You can watch the episode here: http://www.gametrailers.com/gametrailerstv.php