The second interview is for another person or group of people to meet you and interview you. The same questions will be asked along with some company specific questions so it is in your best interests to review any company material you can find before the second interview.

The question concerning why you want to work for them is because they want to know. Why do you want to work for them as opposed to another company? Why did you pick that company to send your resume to? What in the job description caught your attention and made you say, "hey yeah, I want to work for them"? Do your like the product they put out? Did they have a cool graphic design on their website?

What you shouldn't say is, "Yeah, well, I hate the crap you make and sell to other people, but your competition really sucks big time and I figure working for you is the lesser of two evils."