1st step.
Install the following mods:
http://fallout3.nexusmods.com/mods/3808/? and http://fallout3.nexusmods.com/mods/16490/?
2nd step.
Make SURE the Unofficial Fallout 3 Patch loads BEFORE the Error fixing mod.
You should use either Fallout Mod Manager: http://fallout3.nexusmods.com/mods/640/?
Or the better alternative, Nexus Mod Manager(Which is a universal mod manager for games like Fallout 3, Skyrim, Fallout NV, ect.)
http://fallout3.nexusmods.com/mods/modmanager/?
OPTIONAL STEP if you want to make sure the mod loading order is good, use the following program.
https://code.google.com/p/better-oblivion-sorting-software/

If you're using a Quad core CPU(Like an i5 or the AMD equivelant)
I seggust changing the following in the fallout.ini file which is located at
\Documents\My games\Fallout 3

Change the following, and the following ONLY
NOTE this is case sensetive, I seggust you copy and paste.


bUseThreadedAI=0

You must change this to:

bUseThreadedAI=1

Directly underneath the changed line of text, create a new line and type:

iNumHWThreads=2

Save the config file and then close. Then try to launch Fallout 3.
Now, what is basically does is telling the engine to ignore the extra cores and run only on 2 cores.
Happy gaming!