This might just be personal perception, but I tend to think of personnel departments as worker focused while human resource departments are company focused. But this might just be a grudge I have with the human resource department at my own company.
I always get the feeling that they are trying to do as little as possible for the people that work there while doing everything they can to shift employee benefits into the coffers of the company. It really feels antagonistic at times. I wish I had an advocate within the company but it feels more like I have an enemy.