I'm currently helping to support a large scale introduction of the ITIL processes (at least some of them) to a large military organization. While there is a lot of focus on the blocking and tacking around processes, supporting tools, and the like, it never seems to amaze me how every one of these adoptions are really exercises in managing organizational change. Perhaps the most important role on your ITSM team is the role of the Communications Manager, because they have to really drive both the client organization and the project team through Kotter's 8 steps to Organizational Change (for a quick read on what these are, see http://www.mindtools.com/pages/article/newPPM_82.htm
The fundamental reality of life is that people resist change for survival reasons. I know how to survive today. If you change something, I might not know how to survive tomorrow. So I resist. If change is forced upon me, I will adapt, lessening the pain (by not complying) where possible.
In an organizational context, this is a recipe for disaster. If you wish to be successful in your project, you must be successful in creating buy-in and real commitment from the customer. This is very simply a game of WIIFM (What's In It for Me?). For every stakeholder, you MUST understand the WIIFM, and communicate (again, and again, and again) and get buy-in to that to gain the trust and commitment of that stakeholder. Many times, this isn't a process issue, or a tool issue, but a political one. What are they winning? What are they preceived to be losing? How do we maximize the benefits and minimize the risks of the change (sound familiar?)