They probably want to have a LOOK at you more than anything. Dress professionally but don't over do it. Remember they are looking for someone to represent them even if you think your job is in the back room. When you talk, don't talk too fast and don't mumble. Look people in the eye, but don't stare. If you have to do problem solving stuff, then methodology is usually more important than getting the right answer so break the problem down logically and proceed. Be respectful but don't cower. Corporate exectutives really don't think anything is "Cool" so don't try to be. They will be more concerned about whether you will be a problem than if you will be a genius. And most of all relax :-). That's my 2 cents.
Good luck.
Let us know how you do.