*Is jealous that you got an interview
I get nervous too, and anxious for those kinds of things. I've been applying to jobs recently too, and haven't gotten any replies back. It makes me feel depressed.
I hope that when you do go, that you're successful; because it does feel really bad to go to an interview and come home thinking that you probably didn't get the job.
What may help you, is to carefully re-read over the original job description that you applied for and to pick apart each thing, and learn about it; so that if you are asked about your capabilities, you can reference it back to the job position.
Also, there are certain questions that are common in interviews, one of them for example is the question asking where you see yourself in X amount of years, or what you future goals/plans are. You can prepare for the interview by researching those questions and knowing the answers (your answers) in advance.
Finally, if the company has a website, or has had other job postings (you can find it by using the email listed in the original job posting that you replied to, usually the email is that of a company member; and I can always find more than one job posting from that email address to give me a broader idea of the company). If the company has a website, look at it, and see what they say they are about, what services they provide, and get a good idea of what they are all about.
Knowing these things; since it sounds like you have a while to prepare; can help you feel more at ease. I find that the less I know about something, the more nervous I am. Like if I don't know what they will ask, or don't really know what the company does; or the position still is vague etc...that I am really nervous.
It's like a test, if a person didn't study beforehand, of course they will feel nervous going in and trying to pass. But if they studied they will feel less nervous, and will have fewer questions to be stuck on. Same thing here; learn as much as you can about these things before the company so that you can go in and not have a blank mind or so that you know what you're talking about more; and thus could talk more confidently.
P.S.
That puking smiley made me smile....though it was shocking; it was rather effective in conveying your anxiety!