Stephen Baxter wrote a book called "Voyage" which talked about a voyage to Mars in the 1980's. It postulated that we could have gone to Mars with such things as a gravity boost from Venus, and better political impetus.
We could have gone to Mars years ago if we had had the political insight and will to do so. Instead we got entangled in wastes of money like extensions of the shuttle program, the international space station, and the 90-day report. The 90-day report was a report NASA gave Bush Sr. outlining the cost of a mission to Mars; it involved a lot of unnecessary garbage like a moon base and space station, and the final price tag was 450 billion dollars. So, obviously, congress didn't even go near it, and the possibility of a Mars mission suffered.
Robert Zubrin says that we could go to Mars with current technology or technology that we have the potential to easily develop. The idea is that we could make most of the rocket fuel on Mars with a little factory that takes the elements from Mars' atmosphere. Anyway, I believe that Mars could have been achievable if we had really spent our money elsewhere, ONLY focused on Mars (as opposed to the idea that we must build a space station or moon base first), and so forth.
Oh, by the way, this is my first post since the new forums started up. I wonder if anyone remembers me from the old forums, heh.