Welcome Karen!
You've come to the right place!
What industry is your company on? How big is your organization (workstation/server count)? What is the old legacy system? How soon is "soon"? How big is the support team you are managing now?
There are tons of information about Dynamics AX on http://www.microsoft.com/dynamics/ax/default.mspx then agan, I believe the best preparation for your team would be to start on learning the application and surrounding technologies pronto!
Good luck!