In Windows NT 4.0, you had to install a new Passfilt.dll and modify the registry, to implement Strong password functionality.
Windows 2000 includes a password complexity library, which you can implement via Group Policy:
1. Open the Default Domain Policy (GPO).
2. Navigate to Computer Configuration \ Windows Settings \ Security Settings \ Account Policies \ Password Policy.
3. Double-click Passwords must meet complexity requirements and Enable it.