I'm sure someone will be along soon to answer your questions exactly.... but I just felt like puttin in my 2 cents.
First of all, good luck on your interview

I'm sure you'll do fine. I'm also sure that 99.9% of all people interviewing are nervous too, and I'm sure the interviewer is aware of that
Second, I've never interviewed for the program, but I will be for Spring 09 so anything I say is just stuff i've read on here before
As far as questions they ask you, I guess it pertains to the roles you are going for. If your going for character attendant, think of the possible situations you could be put in, and have ideas ready as to how you would handle them. I guess you could use that advice for any role you are going for. I've heard they ask you if you would be willing to work in other locations, other than what you specify, too. It's important to be honest with them. FOr instance, if they ask you if you would ever want to work costodial and you say yes, when you really dont, you could be put in that position and be miserble. It's really important to be yourself, too. You don't want to be fake in the interview.
Don't worry about 'sounding like a dork'. I would just focus on making it aware that you know what you're talking about... have some Disney knowledge in regards to where you want to work... and be yourself. Obviously you will want to be poilte, too
As far as being a "super" senior.... my understanding is that as long as you are enrolled in a college at the time of your interview, you are fine.
Again, I'm sure the alum's will be by here soon to clarify!
Just remember to breathe

You will be just fine! and GOOD LUCK!!!
EDIT:::: I knew it would only be a matter of time before Joanna was replying

She's way too helpful!