Im only guessing, but this is how id do it:
1) Add stuff into the game through the console
2) Arrange them to your liking
3) Take a screenshot
4) Repeat
5) Mux images into a movie with fade effects between the images
6) Record own voice describing player actions in relation to the...
I want Satan character somewhere in the wasteland who gives you 1000 caps for every children you have killed in exchange of some proof off the childs body.
EDIT: Also, the lowest karma level you can achieve is pathetic: Very Evil, Ne'er Do-Well
I want to be Spawn of Agonizing Screams! Or...