In many cases, on campus recruiting process is like what Jerz described.
However, other firms get HR to do the initial work (whether it's application/resume collection, initial review of applicants to invite for interview if space is limited etc). In some cases, 1st round of interview is with a HR rep. (If not, HR rep is in the waiting area of the interview rooms during OCR to answer your questions, to ask you to complete paperwork - before you enter the interview room with current executives)
Then once HR narrows down the number of candidates, current managers and other executives interview the applicants in the next few rounds.