The old FO games (including NV) are *very* crashtastic, since Bethesda's engine was not well designed. Did you know that "bullets" are considered "spells" by the engine? It's held together with duct tape.
Mods address some of the instability; I don't have my mod list on me (at work), but the general rule of applying any unofficial/stability patches & script extenders go a *long* way to enhancing stability, since the community did a solid job of fixing most of the engine bugs.
The last time I played the game was *mostly* stable, though there were occasional CTDs, and one very specific crossroads where the game *always* crashed for some reason.