Haven't installed any codec packs but thanks for the heads upsony vegas is incredibly sensitive to system codec configurations. if you've ever installed any codec packs, you're basically boned.
as a general rule, avoid codec packs. if you've already installed one, you might have to reformat and reinstall your system. uninstalling the codec packs won't work. there's probably a way to fix this by editing the registry, but i haven't be able to.