is it okay to say this on an interview?

C'mon, give the NM a little credit :chuckle -- s/he's not asking that question just to hear you say, "I've always dreamed of working on a tele/neuro unit"!! The question is asked to find out more about you and your professional goals and interests, and to help judge how good a fit your interests are likely to be with the needs of the unit. The question is also asked to see how much "homework" you've done before coming to the interview; do you (the interviewee, not you personally) have a clear idea of what appeals to you about that unit, or are you just looking for a job, any job?

I think it's fair and reasonable for new graduates to say that they don't have a clear idea of a career path when they're just starting out, and that you don't care about what type (specialty) unit you work on as much as getting good support and experience to grow and develop as a new nurse. One thing you can do is ask a lot of questions that indicate you're interested in finding out about the unit and whether it's going to be a good "home" for you as a new grad. And there's nothing wrong with talking about wanting to develop a sound foundation and basic skills/competence -- you can do that without also suggesting or implying that you're going to leave for some other specialty area the first chance you get! :)

Since you've already been on a few interviews now, and are finding out what kind of questions get asked, you may want to spend some time at home working on preparing answers to the questions you know you're likely to get asked in future intervews, so you're not starting from scratch each time you interview. As with everything else in life :), you'll get better at it (interviewing) and more comfortable as you get more experience.

Congratuations on graduating, and best wishes for the job hunting!! :)