Just to follow up on deep thought's thought, there is no coincidence whatsoever between the naming of the ship and Conrad's novel.

Nostromo (the novel) is about the fictional state of Costaguana, where men are battling for power and a fortune in hidden silver. The title character is Italian sailor Nostromo. Like the country itself, Nostromo is consumed by greed and corruption. To spoil the ending of both Alien and Nostromo, Nostromo is destroyed by the appetite for financial gain and glory. In death, the secret of the silver (and alien) is lost forever (or until a sequel is made).

The relationship between the movie and Conrad is perhaps rammed home when Ripley escapes Nostromo in a shuttle named 'Narcissus', a reference to Conrad's The Nigger of the "Narcissus"

By the time Aliens is released, there is no irony in the ship being named USS Sulaco after the central town in Nostromo. It is also worth noting that Alien director Ridley Scott's first major film, The Duellists was based on a Joseph Conrad short story.