The Raider Retreat Mission is an official release by Relic. The Raider Retreat mission is actually a mission set after mission 4 which did not make it into the final cut of Homeworld, however it was fully completed and later released by Relic due to popuar demand.
The full version is the complete standalone release extracted from the disc that came bundled with Cataclysm. This was obtained by myself in 2001. I removed a few directories such as the installation folder for DirectX and Adobe Acrobat to save download time. Scans of the disc cover are also made by myself.
Alternatively there is also a light (lite) version available which requires you to have the full version of Homeworld installed. This version was originally made by Mac_Bug. With permisison, I made a few changes to the readme file to make it easier to follow. It requires moving files from your Homeworld directory into the Raider Retreat folder therefore you must have a full version of Homeworld to use the lite version. If you are unsure or don't want any problems, go for the full version. If you're on a 56k, perhaps try the light version.