Mudskip said:
I have a suit but it's a formal dress suit that I last wore to a wedding. Would that be a bit too much?
If it's along the lines of a business suit, then that's fine. Make sure that it's ironed, your shoes are clean, and be well-groomed. In spite of this day and age where people like to pretend that they don't have prejudices: they do. And having said this, first impressions matter.
Earlier it's been said that you should research your preferred trades. That is very sound advice. You don't need reams of info, but a basic understanding helps. And during the conduct of the interview, relax, but don't slouch. Maintain eye contact, and for the love of all that is holy, if you have a cellphone, iThing or Crackberry, TURN IT OFF PRIOR TO GOING IN. If you nod to everything he says, muttering "uh huh" as you text away, you will make a very lasting impression; however, it won't be the one you want.
In summation, as someone said earlier: this is a job interview. Treat it as such.
Tell us how it goes, and I wish you the best!