Please re-read this carefully. All of the information is included.
Uninstall any codec packs on your system and download the latest CCCP beta release (
http://www.cccp-project.net/beta/). Fallout 3 will then use FFDShow to render the audio. Some people have had crashing problems with FFDShow. Try the beta and the normal release. You can add Fallout3.exe to the exclusion list (open up the "FFDShow Audio Decoder Configuration" program, choose the "DirectShow control" option, and add Fallout3.exe to the "Don't use ffdshow in" field) to continue playing.