You mean the film set in the Alien universe by Alien Director Ridley Scott? James Cameron did Aliens and, to my knowledge, has nothing to do with Prometheus. Besides, he's busy working on Avatar 2 and 3. Fox was bugging Ridley to come back and direct another Alien sequel, but he agreed only on the condition that it could be a film set in the same universe, not a sequel. I can't really say I blame him, after what they did to the franchise with Alien 3 and Resurrection.
I've seen the trailer, but I don't go to movie theaters anymore. However, Prometheus is one of the few films I'm actually looking forward to this year. I'll see it when it comes out on Netflix.
BTW, for anyone who hasn't seen the latest trailer:
http://www.youtube.com/watch?feature...&v=HHcHYisZFLU