It really depends on the interview. Some people only want to see pristine finished work. Some people assume that young designers don't just pull pristine finished work out of thin air and want to know how it came to be and who else helped. Do some research on the interviewers, make a process book, take a sketchbook, and be prepared to show what you think will work best.

Thank you, this is very helpful. That was it, I was debating on bringing my sketchbook, since I am a young designer. Thank you again.

Depends on the situation, but in general I wouldn't do it for every project in your portfolio, but if you wanted to show your thinking process for a few of your projects I think that would be fine.

Just keep in mind in that interviewers are usually busy people and you want to quickly show them your best work, rather than a lot of ideas that didn't pan out.

Good thoughts, thank you. You are pinpointing my thought to not give too much unnecessary background, and only give enough when needed.

Related:
http://typophile.com/node/80454