For minimal security, none of the Windows NT security features are used. In fact, you can allow automatic logon to the Administrator account (or any other user account) by following the directions in Chapter 12, "Configuration Management and the Registry," of the Windows NT Resource Guide. This allows anyone with physical access to the computer to turn it on and immediately have full access to the computer's resources.
By default, access is limited to certain files. For minimal security, give the Everyone group full access to all files.
You should still take precautions against viruses, since they can disable programs you want to use or use the minimally secure computer as a vector to infect other computer systems.