Codec packs like that are not really good. They just throw a bunch of codecs together and let you pick through a bunch of them during install, most of which are for the exact same thing. If your not careful, you can screw things up with them.
The CCCP uses only the relevant DirectShow filters for anything that's needed, and comes with optimal settings. And you don't have to use Media Player Classic with it, Windows Media Player, as well as any other player that supports DirectShow will work with it. But MPC is one of the preferred players. Please look over their FAQ, it can explain it much better than I can.
Now, with 867Mhz, you should get good playback. Unless your using on-board video. If you are using onboard, getting a cheap video card can help you quite a bit.