In Windows 2000 and Windows Server 2003, a new location is added for storage of user-specific file type associations in the following registry key:
The user interface (UI) still points to the global settings in the HKEY_LOCAL_MACHINE\SOFTWARE\Classes registry key. In addition, security is changed so that only members of the Administrators or Power Users group have permissions to this dialog box. This affects workstations, servers, and servers in Remote Administration mode.
On computers running Windows 2000 Terminal Services in Application Server mode, the UI may be locked down so that no one can change file type associations (not even administrators). This is done so that you can only edit the entries programmatically or by using MSI-based applications. This ensures that an inadvertent change in the UI does not effect the global file type associations across the computer running Terminal Services and all of its users. When this policy is enabled, the New, Delete, Change, and Advanced buttons are unavailable on the File Types tab of the Folder Options tool in Control Panel.
You can enable this functionality by changing the following registry entry:
Currently, there is no way through the UI to change or edit the user-specific file type associations stored in the HKEY_CURRENT_USER\SOFTWARE\Classes registry key. If you want to do this, you have to directly edit the registry or develop your own UI to gain access to this information.
For more information, search on HKEY_CLASSES_ROOT in the Technical Reference to the Windows 2000 Registry in the Microsoft Windows 2000 Resource Kit.