To add a plugin to SAP2000, use the "Tools > Add/Show Plugins..." menu command.
If adding COM plugin, enter the exact name of the plugin, which typically corresponds to the name of the DLL file. Finally, enter the text which will appear on the Tools menu.
If adding .NET plugin, click the "Browse" button to browse for and select the plugin .NET DLL file. Then click the "Add" button. Please note that .NET plugins will be available for a future version of SAP2000.