1. Dress appropriately, with "appropriate" being relative to the job.
Obviously, this isn't an office job, so complete formal attire would actually be somewhat inappropriate. If the job requires you to wear, say slacks, wearing slacks to the job would be a good idea. But if the job allows you some leniency, dress how you normally would in the context of the job, but in a presentable manner. (i.e. if the job allows you to wear jeans, and you intend to wear jeans, wear them to the interview, but make sure they are clean and free of holes.)
The point of how you dress during the interview is to give the employer an idea of what you will look like as an employee.
2. Know what you're talking about, or at the very least, sound like it.
Since you are working at a zoo-type-thingy, be familiar with the kinds of animals, research them, and show you know how to take care of them if a question comes up about them.
This is somewhat like the "research the company" tip someone else gave earlier.
3. Know your customers.
Since this is a zoo-type-thingy, it's safe to say there will be kids around. I don't know to what extent you will interact with them, but it would be safe to know how to act around and towards children. Personally, I can't stand them, so you'll have to come up with your own answer on how to do that.
4. Be cool, brotha.
Be yourself. Pretty esoteric an answer, I know, but lying or being nervous won't help you. From your wording above, it seems you are pretty excited to work there. Really let that shine through during the interview, but if there are other reasons you are getting the job (to compensate for a lost scholarship, like I am, or just to have some more spending money) let the employer know. The employer probably won't think you are less deserving of the job than someone else and in fact may give you bonus points for honesty.
To be honest, I've never actually applied for a job myself, jobs just seem to come to me. That said, I think my honest and kind nature is what draws employers to me. I actually gave a mock interview in my college class one time, and my teacher said "That was one of the best presentations I've seen in this class; if you was an employer, I would hire you in a hearbeat.)
So as I said, haven't had an interview myself, but to an extent I know what I'm talking about and I hope this list helps you get your job.
Good luck, space cowboy.
(Also, if you have any other questions, feel free to e-mail/instant message/ whatever-they-call-it me.)