Has bethesda posted a description of what the graffic setings do? The grafics concile that can be axcesed from the falloutlancher.exe has many setings i dont understand and so far ive been unable to get the resualts i want. Actuly if i could just get rid of the all the smoke it insists on rendering id be most hapey. Beyond that i have some pie in the sky dreams of halting the day night cycle and all of the darkness in general of this unbeliveable black screen game, but that would just spoil people i spose.

This site has some side-by-side picture examples of a few of the graphics settings, and a text description of some others:
http://www.tweakguides.com/Fallout3_5.html

This one shows examples of low-med-high-ultra settings:
http://www.pcgameshardware.com/aid,665387/Fallout-3-Graphics-settings-compared/News/

As to the particle effects and changing the day/night times, there might be mods at the Nexus to alter them. I don't know much about the available mods, but you could always ask in the mods forum.

http://www.gamesas.com/index.php?/topic/1116998-fallout-mod-detectives-9/