What year in the future does ALIEN take place?
It takes place in the year 2000. 
Heh, I always felt like the Alien series was set in an alternate universe where space was colonized in the 1930s. Did anyone notice the antique plumbing in Alien 3?
I believe that Alien took place in 2122 and Aliens in 2179, this taken from various websites. I can corroborate it in the near future if I can dig out the Aliens RPG sourcebook, but I have no idea where I’ve left that.