The Complete Aliens Omnibus: Alien

Original Sin
by Michael Jan Friedman 
Centuries after the death of the original Ellen Ripley, her clone has joined the fight against the Alien threat. With the help of an android named Call, a brutal hired gun named Johner, and a paraplegic mechanic named Vriess, she will battle an Alien horror, and discover the answer to a question that pierces the Alien mystery to its seething acid-chamber of a heart. 
DNA War
by Diane Carey 
In a bleak galaxy, the hospitable planet Rosamond 6 is a rare find. But while it may look like an oasis among the stars, it harbors a fatal secret: it is infested with Aliens. Eager to prove her theory that the Aliens can be reasoned with, anthropologist Jocasta Malvaux has set up an observation post there. And something unexpected happens: the Aliens don't attack. But, why? Could it be that the monsters are evolving? Or is it a matter of time until every person on the planet must fight for their lives?