Just picked up New Vegas on Steam, installed a few mods once the game installation was complete. In the 'Data' folder I merged some files into both the 'Menus' and 'Textures' folders, which is when the game went from working fine to refusing to launch. Just looking for a way to download/reinstall those two folders with original data.

Just disable the mods, the game reads from the .bsa files, not the folders.

Crashing on launch usually means you're missing a master. ie: another mod that one of the ones you downloaded requires to work.

Suggest you check the readmes of the mods you grabbed.

Tried disabling the mods, no success. Read the readmes, I figured out that I must have merged the MTUI mod files in with those folders, which (I think) is my problem.

Never mind, I'm just going to reinstall the game.

Delete those folders and then tell Steam to verify the game.

It will download anything you are missing.

Which should be nothing, since the game doesn't keep its models/textures/menus in loose files.

True, but you used to get a few in patches from Bethesda, and it's possible they may do that with NV as well since it would avoid re-downloading the entire BSA to replace a few files.

The verification doesn't take long.

Only issue might be it resetting the INI files, which could be a benefit as well.