What Video Player to Use

What video player do I have to download to watch any kind of streaming video from the web. Also is there is setting that I need to change in safari. I may be wrong here, but isnt QT the default player on Mac. So will it play all kinds of streaming videos. I tried to watch a video for a movie thats on my schools website, when I play it on a PC and click that it opens on Windows media player, but on my MB it does not? Any suggestions.