Download Location: SSP-Platform-2-4-0.zip ("SSP Platform" is a portal application which acts container for SSP itself. The two applications are versioned independently. By default, version 12.54.0 of SSP Platform will include version 2.4.0 of SSP.)
Unzip the file into a suitable path (e.g. on Windows C:\ssp\platform-src or on Unix/Linux/Mac /usr/local/ssp/platform-src)