CodecInstaller

codec_installer.png Looking codecs for your movie files? No sweat.
Donationware CodecInstaller is your answer. For Windows, this little application basically scans the movie you’re trying to watch and analyzes it for which codec you would need. Then it brings up a list of the codecs that it can install and which one matches. If you want to install all of the codecs, you can tell it to do so, or you can install the ones that are particular to the movie file you’re trying to watch. Either way, it helps you out in identifying and eventually watching the video file instead of trying to figure out the differences between xvid and divx if you don’t already know what those codecs are or do.
Another great thing about this? It tells you which company the drivers are from, where they are installed and what version it is. This allows you to check against versions and if you have different codecs from different companies, to actually make sure and determine which one you actually have.
Lifehacker < CodecInstaller