Actually "Zeta Reticuli" is a real binary star system in the Reticulum constellation. (presumably "II" is the designation of the second star in the system).
The actual planetoid (it's very small) is called Acheron in the novelization of Alien but called "LV-426" in dialogue in Aliens.
Hey Phase, I'm quoting the director. And I thought everyone here including myself came to the conclusion that the planet that Prometheus lands on is NOT LV-426. If the Nostromo was close to the system, and the derelict came from the planet that Prometheus lands on which is in Zeta Reticuli, it's still a relatively short trip.