Well, there was that old AvP spec script that's been online for eons. It pretty much lifted the entire plot from the original AVP comic (Peter Briggs siad it was 'inspired by') but I think there were some legal issues with that. And, of course, Paul Anderson has ideas of his own. Dark, twisted ideas. Ideas that...well, suck.
I can even swallow setting the film on Earth to keep the budget down, but they then go and build all of these pyramid sets. That money couldn't make something otherworldly as a setting? How much does this film cost, anyway?