Filenames with a .plt extension contain PLT Scheme archives. To install a .plt file you can use the "File | Install .plt file..." menu entry in DrScheme, which allows you to enter a file name to install or a direct url of the .plt file. In addition, you can follow the directions for your platform:

Windows

Double-click on the downloaded file or drag the file onto the Setup PLT.exe executable in the plt directory.

Macintosh

Drag the downloaded file onto the Setup PLT application in the plt folder.

Unix

In a shell, run

    plt/bin/setup-plt filename.plt

You must have permission to write the files contained in the archive. If your PLT installation is in a system directory, typically the archive must be installed from the root account.