I'm looking to use the land /buildings in Fallout:NV to do a small mod that is not in the Fallout Universe. What is the easiest/best way I could wipe out the people and mobs from the overworld landscape so I can proceed to add my own custom characters in? Is there a way to dupe the landscape/buildings without the people?

It is easier to create another world space and link it to the current.

Ok. But what is the fastest way to create another world space without having to customize terrain etc. I'm basically looking to get a sandbox environment of a small area of the world so I can add my own NPC's / mobs.