I didn't realise that some people had answered a similar post a bit earlier. See the post called 'playin movies- pls help'

Another program that might help you is mplayer found at:
http://mplayerosx.sourceforge.net/

VLC is found at: http://www.videolan.org

Hopefully either of these programs will enable you to play what you have if you can not play them using QuickTime player. Good Luck!