An HRM interview may be similar to other MBA interviews, but it's likely that you'll be asked "Why HR?" If you have experience in the field or have studied HRM, it will be easier to answer this question. However, if you're switching fields, you'll need to explain your interest in detail. It's important to stay honest and not try to deceive the interviewers, even if HR isn't your first choice. The rest of the interview process will be similar to other IIM interviews.
One student with a finance background shared his personal experience of being asked this question during an HRM interview, even though he had already received offers from other IIMs and HRM wasn't his first choice.