Try looking at the settings in VLC,when you install VLC you have the option to make it your default player for a whole range of file types (Similar on widows media player but not so many choices)
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Also if you use 'Search' on forums and type in VLC you will see that it comes highly recommended by a lot of people, and it plays more file types than many other players, and lastly (Which I like) it uses far less CPU than other players. hope this helps
N2