Realistically it's not going to happen, if by "career" you mean "source of enough money to live on" and not "thing you're primarily known for doing". In fact, if I may speak from experience, writing in general isn't going to do it. John Scalzi (he of the unorthodox career trajectory, of which more anon) made $67k last year as an SF writer. That's really good for an SF writer, but it's about entry-level for, say, a computer programmer.
The telling detail for me came during the discussion of conventions. Many fans who are heavily involved in the SF community are perfectly capable of writing professional-quality SF. They don't do it because they're happy making 10 times the money as theoretical physicists or sysadmins. In other words, they're rational.
But of course lots of people, including most of the VP instructors, devote big chunks of their lives to and are best known for writing science fiction. How do they do it? Here are the tactics I discerned.
James was talking about how you can get paid for the same story multiple times (anthologies, basically) and how that money adds up, but I can't see it adding up to very much unless you constantly write stuff for anthologies. Which, of course, you can do.
One thing that doesn't work is selling movie rights to your book. Steven Gould's Jumper has been turned into a big-budget Hollywood movie (I hear tell it takes place in a world) and he certainly got a chunk of money from that, but it's not life-changing money. It's money for paying off a big one-time expense like a kid's college education. Selling one set of movie rights is not fundamentally different from selling one novel. If you want Hollywood money you should go into Hollywood proper. Sat Oct 20 2007 23:37 Making a Living:
Part III or something of my synthesis of knowledge from Viable Paradise. I'm trying to go beyond a simple chronology, which others have provided ably. Tonight: a bit on what I heard about SF writing as a career.