I don't think it's jinxing the whole thing... As has been said already, if something is going to happen, it will happen regardless.
As for me, I didn't want to start thinking of names until I knew the sex, because I thought that if I picked a boy's name and a girl's name, I might prefer one of them, then I might have a preference of the sex of LO. So I waited until I knew I was having a little boy, and OH and I have come up with a name we both love. Now I can't imagine calling LO anything else when he's born!
xx