nFront Account Disabler is a purpose built service that disables user accounts that have not logged on in a specific amount of time. It seems that such a procedure could be easily scripted. However, there is the challenge of discovering the true last logon time becuase each domain controller keeps an indpendent value for the last logon time. For example, you may have logged on in New York at 8 AM today, but your last logon to a Los Angeles domain controllers in 3 months ago.
Installation is very straightforward. It is simply a service file with a GUI for configuration.