So I just installed Old World Blues on Steam, and it says on Steam it's installed, but on the launcher for FNV it doesn't show up on the list of data files, and on the main menu it isn't on the list of downloadable content.

What do I do?

I have this problem too.

I bought OWB, and from the looks of it... It only downloaded the sounds?... Not the ESM, meshes, textures or anything like that. The only OWB-related file in "Data" is a BSA file called: "OldWorldBlues - Sounds"

Try validating your game files (right click NV, properties > local files > Verify Integrity of Game Cache). That's what I did and now Steam is "re-aquireing" a 2mb file. Hopefully its Old world blues...