Well first your on 'LION' they are still writing the stuff for it and even the companies that are Apple friendly are working hard to get the updates and the fixes...
Look at first getting Perian http://perian.org/ a MUST have plugin.....
Then look at the following and get their updates as well....QuickTime third-party component page
http://www.apple.com/quicktime/resources/components.html
Their site
http://www.divx.com/en/software/download/start/mac