Original Cast in Nostromo Edition Pre-Order DLC
No Ian Holm (though Ash will be in it).
There will be two missions. The first lets you play as Ripley, Dallas or Parker shortly after Brett dies. The second is just Ripley as she scurries to hit the self-destruct and make it to the escape pod. Er, spoilers.
I am very excited about this. They're calling it a pre-order thing, but they use the phrase "upgraded to the Nostromo Edition" which makes me think this will be in every first run version of the game. I don't know that I'm going to take that chance, though.
Look at this: