H.264 codec is apparently built into Windows 7, but there appear to be some severe restrictions placed on its use. By installing DivX and Xvid packs, you can ensure that you have a proper set of updated codecs. VLC Media Player is also excellent for supporting all types of video formats that Windows Media Player and other video players are not compatible with. It is also light-weight and low on resource consumption. You may find that installing codec packs can cause conflicts with some games or video editing software, but this is a very minor problem which only seems to occur in some instances. Overall, you should have better luck trying these options. Let us know how it goes.