If the answer is, 'No, I'm not offering you this job right now, I still need to know your salary requirement' then you have to discuss the issue. However, instead of giving one figure, give a range with the low end of the range generally about what you would like to make. First, that you know what you're doing. You've thought your position through, you've done your homework, and you're comfortable with your decisions. Second, that you have the skill to negotiate.
Most employers realize that negotiation can be an art form.
Of course, the bottom line is you should have, through research, a pretty good idea of what the job is worth before you go into the interview. Talk to people who are doing the same type of work in the same geographical location. They will often give you a general salary range for their positions, or you can get on the Web and browse through salary surveys. Let's say the interview process has gone smoothly, you've gotten a job offer, and you've had your first discussion about money. Once the job offer has been made, you can say, 'I appreciate that offer, and I agree with your assessment of my impact on this organization.