You're right - it's strongly implied that the company has had previous contact, but we have no information about any previous expeditions. Presumably there was one.
Recently, Ridley Scott started making an Alien Prequel movie. He said it got into the story of the "Navigator" (Space Jockey) and there were also human characters. So presumably the very story you want told.
The film is still being made, BUT - it's no longer officially an Alien Prequel. It will be called Prometheus, and apparently still is roughly along the same lines, but I imagine the continuity doesn't quite jibe with the previous films.
I know they hired Giger to do the design work, and I know that he hates to repeat himself. So my guess is that he turned in fantastic stuff, but that was so different from the existing creatures that if it was labeled as an Alien movie the fans would revolt.
Personally I'm glad he's doing it as a new thing. Sequels are okay to a point, but the movies really need more original stuff...