This is a great question, notadmin23, and one worth considering from a couple of different perspectives:
1) Ad Coms: Ad Coms ask this question largely for two reasons: (1) to make sure that the students on campus represent a diversity of future career paths and, (2) to make sure you know why you're going to business school. For the first, there is no right or wrong answer; they really want to know where you're going to fit in terms of the overall balance of the class. For the second, they want to know that you've really given your future career some thought and that you're not just looking for a two year vacation. Recruiting at business school generally happens at break-neck speed and, if you haven't some clue where you want to go, it's easy to get completely overwhelmed by the process.
2) You: See the last point above. Even if what you really want is that two year vacation, you are going to have to contend with the realities of the B-school job market very soon. If you don't know what your career aspirations are, recruiting can be a very trying time. So, put some thought into this before you show up; you'll be happy that you did.
In terms of specifics, it's nice to know what the short- and long-term plans are but you don't want to be overly defined. You want to appear as highly employable, not just committed to one specific job at one specific company. Speak in terms of functions, industry, types of companies. This keeps your options focused but your potential employers broad.
Hope this is helpful and best of luck in your application process,
MBA Prep School