It's a misconception that you need to install bloated codec packs (and unnecessary too) Long term, this will create confusion in Windows page-ranking codecs system for playing media files. You should really check out what you NEED first, using a codec-viewer/checker.
For a start, as an all-round general-purpose splitter/filter, install FFDShow multi-purpose (Read below)



Then go here ... http://www.doom9.org/
Go to downloads, and scroll down to find FFDSHOW ..
Install that and reboot. That's a good start. Post back if you need help with any others!

Something nifty like this on the system will show you what's installed for different formats ...