When you begin to rollout Windows 2000 platforms in your Windows NT 4.0 environment, you will inevitably detect the presence of this contagious disease.
When your Windows NT 4.0 clients experience the Windows 2000 environment of their office mates, even with the Classic shell, they will quite naturally start to complain, lobby, agitate, etc.....
If you are planning an extended rollout, you might consider forcing your Windows 2000 clients desktop, to look exactly like the Windows NT 4.0 desktops that they replaced, until the rollout is complete.
If you implement the Enable Classic Shell Group Policy, at User Configuration\Administrative Templates\Windows Components\Windows Explorer, it will disable Active Desktop, Web view, and thumbnail views, as well as preventing the configuration of single-clicking. Users will NOT be able to restore these features.
NOTE: This policy takes precedence over the Enable Active Desktop Group Policy.
If the policy is NOT Configured, it can be implemented by setting the ClassicShell value name, at HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer, a REG_DWORD data type, to 1.