Make sure you have Source SDK Base 2007
- Install the mod (obviously) http://release.blackmesasource.com/
- Make a folder called Black Mesa.
- Go to Steam\steamapps\sourcemods\BMS
- Copy the materials, models, maps and script folder to the Black Mesa folder.
- Put it all in to addons.
That is all. 4.78 Gb was to much to upload.
The maps are gorgeous