I actually have a strong interest in creative writing too, although my main ambition is to become an astrophysicist/astronaut. I think I am probably going to double major in astronomy or astrophysics or physics with comparative literature (because I want to integrate intensive foreign language/literature study into my college career.... and because the US no longer has much of a space program :P). I think I am going to try to have a concentration or minor though specifically in creative writing. That way, I will have a well rounded career, and I can pursue both astrophysics and writing (and maybe publish some science fiction writing). I think the double major is your best bet- and you get the best of both worlds.
I also think that most english departments would probably allow you to concentrate in both creative writing and professional writing, if you would choose to do so.