Introduction to modding
Modding is the process of altering or adding to a computer game for the purposes of providing a different and/or improved experience.
With Fallout: New Vegas, Bethesda has provided the G.E.C.K. to fans, a set of tools developer Obsidian used to create the game. With these, one can create mods for the game without too much trouble, though possibly a lot of work depending on the scope of the project.