Ive figured out how to use meshes and textures from NewVegas in Fallout 3.
NVIMP.ESM MEGAUPLOAD - The leading online storage and file delivery service
You need the Fallout - Meshes.bsa and the Fallout - Textures2.bsa from the ps3 version of NV (you dont need the Fallout - Textures.bsa because from what ive seen its just the fallout 3 textures + the fallout 3 dlc)
Use the ESM file provided (it only contains the unique 9mm and a hunting shotgun as proof of concept) and place it in the DATA folder of your Fallout 3 directory
Rename the 2 .bsa files to NVIMP - MESHES.BSA and NVIMP - TEXTURES2.BSA and place them in the Fallout DATA directory
Now you edit the FALLOUT_GOTY.INI
First make it look for NVIMP.ESM:
Now edit the essential file cache list to:
sEssentialFileCacheListE=DATA/MUSIC/SPECIAL/MAINTITLE.MP3, DATA/FALLOUT - MISC.BSA, DATA/SYSUTIL/*.PNG, DATA/ICON0.PNG, DATA/PIC1.PNG, DATA/FALLOUT3.ESM, DATA/UPDATE.ESP, DATA/ANCHORAGE.ESM, DATA/THEPITT.ESM, DATA/BROKENSTEEL.ESM, DATA/POINTLOOKOUT.ESM, DATA/NVIMP.ESM,DATA/ZETA.ESM
Finally change the SArchivelist to this:
SArchiveList=ZETA - MAIN.BSA, POINTLOOKOUT - MAIN.BSA, BROKENSTEEL - MAIN.BSA, ANCHORAGE - MAIN.BSA, FALLOUT - TEXTURES.BSA, FALLOUT - MESHES.BSA, FALLOUT - VOICES.BSA, FALLOUT - MENUVOICES.BSA, ZETA - SOUNDS.BSA, POINTLOOKOUT - SOUNDS.BSA, BROKENSTEEL - SOUNDS.BSA, THEPITT - MAIN.BSA, THEPITT - SOUNDS.BSA, ANCHORAGE - SOUNDS.BSA, FALLOUT - SOUND.BSA, FALLOUT - MISC.BSA, DATA/NVIMP - MESHES.BSA, DATA/NVIMP - TEXTURES2.BSA
Now your copy of Fallout 3 will load textures and meshes from the NV BSA files.
The unique 9mm pistol is on Ian Wests bunkbed and the hunting shotgun is on the floor of the male bathroom in megaton, ENJOY!
NOTE: There are 2 problems ive came accross.
1: NewVegas added some animations that arent available in fallout3 (i havent figured out how to import them yet) so you may have to play with the reload animations a little to make them look right.
2: The game WILL lag like a mother****er if you have other mods enabled that use the content from more than one fallout 3 dlc (so dont use mods that use meshes and textures from both ZETA and THE PITT for example).