Things You'll Need
Instructions
Download a "Project 64" plugin. The official forums have a thread listing all "Project 64" plugins and their links.
Unzip the plugin. If you do not have an unzipping program, download and install one. "7-Zip" is entirely free, and the similar program "WinRar" has a one-month trial.
Open "My Computer" and navigate to your "Project 64" directory. By default, it's "C:/Program Files/Project 64." Open the "Plugins" sub-directory.
Drag and drop the plugin files into the plugin directory. The files end with ".dll."
Open "Project 64." Click "Options," "Settings" and "Plugins." Select the plugin you want to install.