First you need to run the ffdshow Audio decoder configuration utility:
- If you installed ffdshow on its own then it should be in Start menu/Programs/ffdshow.
If you installed it as part of a different codec pack it may be listed under the codec pack (e.g. CCCP or Vista Codecs).
You might also be able to access it directly from the Run menu (windows key + R):
'C:\WINDOWS\system32\rundll32.exe ffdshow.ax,configureAudio' or
Depending on your media player version and how you installed ffdshow, you may be able to access it via Windows Media Player, menu > Tools > Options, DVD, Advanced.
Failing that, run a file search for ffdshow.
Hit 'Ok' once you're done.
In some versions of ffdshow the exclusion list is under 'Info and debug':
Now you need to run the ffdshow Video decoder configuration utility and do the same thing.
Your X3:Terran Conflict should now be ffdshow-free!
EDIT: Added comments by Greyward, Spamas and Wolf-R1.
EDIT2: Added WMP method (courtesy of Terre).
Edit3: Replaced outdated image links (old links: #1, #2). X2-Illuminatus