Various things that help Fallout 3 to avoid crashes on windows vista.
My notes, derived from list below and some other things I've done:
Reinstall your PC's .net 3.0 distribution by going into Programs and Features, clicking Turn Windows Features On or Off, and then unchecking the .net 3.0 box. After closing the panel and allowing it to complete, do the same thing and recheck the box. Fallout 3 installs a BETA version of .net 3.0 which is not stable. Reinstalling gets it off your system.
In relation to the above note - it also helps to completely uninstall .net framework v3.5 from your PC (and leave it uninstalled as long as you want to play Fallout 3). It does not appear to be compatible with fallout 3, and will generate crashes even when .net 3.0 is installed correctly. If you have programs you need to use that require .net 3.5, the only workaround I can think of is to keep the redistributable package on your hard drive and reinstall it whenever you need to use those programs.
Reinstall your PC's visual C++ 2005 redistributables, both x86 and x64 if you are running windows vista x64. Link to the redistributables on the sidebar. Same reason as above - Fallout 3 uses a BETA version of the VC++ redist which is not stable. Reinstalling it gets it off your system.
Reset your controls to default at the game's main menu and get used to playing it like that. Curiously, many people have reported that this stops some crashes to desktop. No logical reason, just seems to work.
It helps whether you own an ATI or nvidia graphics card to set your desktop resolution to the same resolution as you play the game in. For whatever reason Fallout 3 doesn't much like running in especially higher resolutions than the desktop.
In FALLOUT.INI (located in Documents / My Games / Fallout3) find bUseThreadedAI=0, and change it to bUseThreadedAI=1. As well, add a new line below it that reads iNumHWThreads=2 . By default Fallout 3 tries to run as many threads as you have cores since it's a multithreaded game, but quite often has a tendency to hard lock on CPUs with more than 2 cores (eg. Phenom II X3, X4, Core 2 Quad, Core 2 Extreme, Core i7)
An addendum to the above - even with this fix applied, having a quad core CPU in my PC causes crashes (confirmed by the use of a dual core CPU - crashes disappeared). The workaround is to use msconfig (click start, type msconfig into the search box, press enter), click on the Boot tab, click advanced options, check off "Number of processors:", and select 2, apply the change, then reboot. When you're done with fallout 3, do the same in reverse (uncheck "Number of processors:") and reboot again to use your extra cores.
In the compatibility options for the actual fallout3.exe file, select run in compatibility mode for Windows 2000, and check Disable Desktop Composition. Click Apply. Many people report that this helps, but compatibility with XP SP2 actually causes more problems, so they selected 2000 and it worked.
In your Steam options (if you use Steam), disable the in-game overlay. I suspect it's not fully compatible with the Windows Live overlay.
If you have any codec packages AT ALL installed, including those that may have come with a third party media player (such as winamp or anything used to play audio / video other than Windows Media Player), uninstall them. Fallout 3's internal MP3 codec appears to be much more stable when there simply isn't any other codecs present. Unfortunately, this means you'll have to watch your media on another PC, at least as long as you want to play Fallout 3.
Make sure the latest graphics drivers for your graphics card(s) are installed. Links at side. Reasons are fairly obvious (fix bugs in the actual gfx drivers).
Quote copied from a forum somewhere:
I have found the primary issues causing the CTD and other crashes. I’ve sent 3 e-mails
1.) Fallout 3 Installer installs an older version on C++ Visual 2005 that appears to
2.) Fallout 3 Installer installs a Beta release of DOTNETFX3.0 (.NET Framework 3.0). For
3.) Fallout 3 Installer installs a non Plug’n Play DRM device manager (not driver but a
4. Fallout 3 Installer installs SecuROM Root kit as well as 8 hidden non Plug’n play
5.) Fallout 3 also has its own built in MP3 codec coupled to its DRM to protect MP3’s on
6.) Fallout 3 has 14 memory leaks that we found. Most are small, but there are a few that
7.) Fallout 3 video graphics buffer needs to be adjustable in the options and an automatic
8.) Most games were fault free with a basic XP Pro SP2 reload, and only Critical updates
Hopefully, Bethesda will address the issues more than 100,000 people are having.