H.D.
I would still dress nice, even if that means a nice pair of slacks (ironed), a blouse (not a T-shirt) and an nice pair of shoes(not sneakers or flip-flops). Comb your hair and put on a light coat of make-up.
This does two things; you feel GOOD about you and you present an air of professionalism. You said it right in your first sentence. =)
Good luck on your interview!!