When dealing with codecs, more does not equal better. Having the least amount on your system is the best configuration.
This is exactly what the Vista Codec Package does for you. You will no longer be restricted to using a specific player. Windows MediaPlayer and Vista MediaCenter will be able to play all your files.
The official change log for version 4.5.6 is as follows:
- update Haali components
- update FFDshow components (multicore patched)
- improve x64 compatibility (AC3)
- update FLV, MP4 filters
You may download this updated version here