cdnaudit is mostly right but there are differences company to company and industry to industry.
In GM and energy stuff it can vary from having no HR involved beyond dealing with them once you get an offer. Others will be all HR people until you get to R2, they will do the presentation (with alums present to answer questions), be the contact for applying, and then will do R1 interviews. Some program managers will be an MBA alum from your school, some will be an MBA from somewhere, and some will be HR...there is definitely no size fits all.
Honestly it doesnt really matter how a company does it, I have seen all the different ways work extremely well but also have seen each be very frustrating. I think its more about the company than only how they structure their recruiting. This year might not be the best example since it was very dynamic with some programs pulling out at the very last minute or even deciding between R1 and R2 to cancel internships.
Kellogg Class of 2010...still active and willing to help. However, I do not do profile reviews, don't offer predictions on chances and am far to busy to review essays, so save the energy of writing me a PM seeking help for these. If I don't respond to a PM that is not one of the previously mentioned trash can destined messages, please don't take it personally I get so many messages I have a hard to responding to most. The more interesting, compelling, or humorous you message the more likely I am to respond.