Interference from senior co-workers

I am a new IT Manager in a respected co. My problem is not technical but is related to management and inter-personal relations. Being the new guy in the co. I lack some experience in the internal procedures of the company, as well as in management in general. Some of my senior co-workers and managers are making use of this to interfere in my work as an IT Manager, and this is really bothering me. All the technical skills and courses you take don’t really help in these situations. Any ideas ?