Interview with buy-side when accepted offer?

I interned at a BB S&T and was lucky to receive an offer. Without much time to accept it and amidst a horrible economy, I went ahead and took the offer. However, I recently got an interview with a top fund, and I'm wondering if I should take the interview. I'm sure they will ask me if I got a return offer etc. Should I go ahead and interview? If so, should I tell them I've accepted an offer and if so, will they care? Thanks