I would like to start playing Descent again. I'm aware the source code was released, however, everything says I also need "game data". I'm guessing this is art, levels, music, etc. I haven't been able to find it. Was it not released with the source? Is there alternative game data (open source / creative commons) out there? I looked at D2X-XL, but it also needs the game data.

You need to purchase the game data:

http://www.gog.com/en/gamecard/descent_1_descent_2/

It was not released with the source code.

pax,
-Chris

Thanks! That clears things up.