There are quite a few people who are having the falloutnv.exe crash error, and I am one of them. If you check the stop error in the event viewer of when the crash happenend there is a good chance that you will find these lines.
Faulting application name: FalloutNV.exe, version: 1.1.1.271, timestamp: 0x4cc0aa87
Faulting module name: FalloutNV.exe, version: 1.1.1.271, timestamp: 0x4cc0aa87
Exception Code 0xc0000005
This specefic exception code is logged because the program is malfunctioning. I haven't been able to fix the problem, and don't bother reinstalling the game (common fix for this specefic code) because it doesn't help anything.