I have WIN 7 / Quad Core / 64 bit, so far I have tried:

1) Editing the fallout3.ini file to make the game use less processor cores. =

Find the line:
bUseThreadedAI=0
change it to:
bUseThreadedAI=1
Add another line after it and insert:
iNumHWThreads=2

2) Downloading a crash fix from Fallout 3 Nexus (d3d9.dll)

3) Running it on a compatibility mode (= win xp/vista)

4) Disabling desktop themes etc. from fallout3.exe file properties.

5) Lowering settings

This only caused little improvement. it still crashes every 1-20 minutes. Has Bethesda ever adressed this issue?
This is absolutely unacceptable. Does anyone have any info on how I can get my 19,90€ back?
Surely they can't charge for a product that doesn't work.

I've done exactly the same thing as OP. Still persistent crashing at irregular intervals: from 30 seconds to an hour. I purchased a box retail copy years back when the game first came out, then recently bought the GOTY edition via steam for all the DLC. I've tried just running the vanilla game with no DLCs or mods, still the exact same problem, regardless. Skyrim on ultra, loaded with mods runs like a dream, but not FO3. I absolutely LOVE this game when it worked. I'm at a total loss now as to how to get this running with some stability on Win 7 Pro. This is one of my most favorite games of all time, and I would hate to see it just devolve into an unservicable scrap heap. Any help, or suggestions would be great. A compatibility and 64-bit patch would be awesome, but thats probably not going to happen

The first thing to do when wanting to run this game is "Install" OUTSIDE of PROGRAM FILES

When you have a steam version you must install steam outside of program files

And yes , even if you have Win 64bit , install outside of (x86)Program files

...

I do not see a usual response to the suggestions from either the OP or the piggybacking member. For the OP, take note of the nature of the forums. This place isn't the official support site. That is elsewhere. This is gamer to gamer discussion.

Before getting upset with *US* in here, follow normal SOP and actually make a proper problem report.

For the piggybacker, you need your own message, unless the OP declares no interest in this one. You also need to include normal diagnostic information, or forget about asking at all.