You obviously have something going for yourself -- were invited, relax. Look at your interview as a discussion, an exchange of information.
Do not feel pressured to go in and accept the job. Think about the interview like this - the company has to prove to you that you want to work for them. The interview is an exchange of information.
In the meantime, do three things:
1. Research the company -- check the internet for info. about them
2) Prepare a few questions about the job
3) Get you interview outfit together
Also, continue to look for employment until the deal is closed and you are employed.
Thanks, good question.