Feasibility of Humanoid E.T.ss

Hi All, I understand that for the sake of good story telling, even in science fiction, the creators sometimes have to ignore facts about the complicated real world (ex. Gravity seems to be the same on every planet in the Star Wars universe). Ridley has claimed that Prometheus is based largely on feasibility, which is exciting but I would like to question the feasibility of finding human looking aliens such as the engineers appear to be in outer space. I've always been a little bothered this notion in stories such as The Green Lantern or even Star Wars where it is taken for granted that there might be other races of humanoid beings with 2 legs, 2 arms, 5 fingers, 5 toes, 1 head, 2 eyes, etc. It makes sense from a storytelling perspective because the characters more relatable to a human audience. But from a hard science perspective I think it is unlikely at best, and actually shows a lack of imagination concerning what form(s) an extraterrestrial 'godlike' intelligence would take on. The original 1979 Space Jockey is such a humanoid, and my hope for Prometheus is that this gets adressed in some surprising and interesting way. In other words, for the movie to be truly feasible, the characters should be really really surprised to find a giant human head on another planet...anyone else feel this way?