I found the fix for one of the freezing problems and it worked for me.
I had played Fallout 3 in the last few weeks and had no problem.
I recently did a clean vista install and also added a new video card. A 1GB 4870 Sapphire.
I started playing F3 and it started crashing. sometimes within five minutes,s ometimes within 15.
So I started looking all over the web for a solution. I did the fddshow trick, the bios problem was only with the 512mb versions of the Sapphire 4870.
Then I found the following link.
http://www.pdsys.org/blog/post/2009/02/07/Fallout-3-VideoDisplay-Freezes-sound-keeps-going.aspx
Turns out the patch for 1.1 breaks quad core support. The game can't handle 4 cores anymore. So if you have a quad core pc and you install the latest patch the game will start crashing. There are instructions on how to fix this.
Open up the fallout.ini file in: My Documents\My Games\Fallout3
Find the line:
bUseThreadedAI=0
change it to:
bUseThreadedAI=1
Add another line after it and insert:
iNumHWThreads=2
This will limit the game to 2 cores and prevent the engine bug from causing the game to freeze.
I tried this and it worked for me. And I have a quad core pc. Also, I didn't have freezing issues before the patch. Only after the patch. I thought the culprit was my new graphics card but this was my problem. After I made the fix, I played two hours without freezing.
So give this a try. It MAY fix your problem.