Mac OSX covers a multitude of systems and also a multitude of machines. I have a G3 with OSX 10.3.9 and no way would I EVER use a PC again
However my machine is a bit old and I cannot play videos at all well which does not bother me one bit or I would have sorted it by now.
Usually VLC will play almost any file you throw at it, so give it a try.
http://www.videolan.org/vlc/