Deloitte really takes care of its prospective applicants. They held a case workshop at my university to prepare students for the actual interview-- the case given was realistic, and very interactive. The interview itself consisted of 2 thirty minute sessions with senior consultants-- one case, one behavioral. The case is interviewer led, and the behavioral is very thorough in terms of the standard types of questions one might expect to encounter in a consulting internship.
Advice: prepare for cases so you feel comfortable, and know your own experiences well (for the behavioral). Also be sure to communicate your own interest in the company.